Burden of Proof
First, since christianity makes the claim that Jesus existed and that he was the messiah, the burden of proof is on christianity to support the claim. It is not up to non-theists or theists from other religions to disprove this claim. Although we can clearly show that there is no evidence, it is not on us to prove that there never will be.
Second, this burden of proof is doubly burdensome for christianity. Not only would one have to provide evidence for a historical figure named Jesus (and not just any Jesus, but that Jesus), but they would then have to go on to provide evidence that this person was actually the messiah. While someone hoping to support such a claim would have to prove each point independently, the arguments I will present apply pretty evenly to both claims, so I will not be categorizing them.
With that established, I will present the problems that I see with arguments made by many christians on this topic.
Historical Evidence for Jesus the Man
This one is likely to be simplest and shortest of the sections. The fact is that we don't have any. We don't have any of his personal writings, nor the personal writings of anyone that knew him (friends, family, neighbors, etc). We don't have an official record of birth, death, marriage, etc.
Christians will mostly likely want to point out that literacy rates during that time were abysmal and that the likelihood of such a record existing, let alone surviving, is negligible. They would be absolutely correct. The problem remains that none of these things exist nonetheless, in other words, they cannot deny that there is no historical evidence for this specific man named Jesus. It may be that some day, we discover something (a diary, census data, etc) that clearly shows that this specific man existed, however until that day, the "evidence" box has to remain unchecked on this particular point.
Some other form of evidence will have to exist for rational belief.
Historical Evidence for Jesus the Messiah
Personally, I don't see how the first argument that I presented can be construed as anything other than a show stopper, but alas, this reasoning is not always shared, let alone recognized.
Again, we find ourselves in a situation in which we have no direct evidence, rather indirect evidence via a myriad of sources. Sources that we might use to find evidence for Jesus include:
* The Gospels
* Eyewitness Accounts
* Early Christian Writings
* Contemporary Historians
* Old Testament Prophecy
If there are others that I should have included here, but did not, please let me know and I'll edit as needed (with full credit given).
Based on my experiences, many people tend to consider the gospels eyewitness accounts. They are not.
In order to be an eyewitness accounts, they would have to have been written by contemporaries to Jesus. They were not.
Some would (correctly) point out that it is not uncommon for oral histories to be passed down for generations before finally being put to paper. Yes, this did happen, however we have no evidence that this happened here. Furthermore, even if we accept this to be the case, we have to accept the very strong likelihood that the story changed quite a bit between the alleged witnessing of events and when they were recorded by whomever it was that recorded them (the anonymous authors commonly referred to as "Mark", "Matthew", "Luke", and "John").
Oral histories with many sources will naturally break down over time (as seen is social experiments such as "the telephone game"), so even if we were to assume that the first gospel (G.Mark) was founded in oral tradition, his telling would have cherry-picked details from a wide variety of available tellings. G.Matthew and G.Luke/Acts are based, in part, off of G.Mark and G.John is mostly a separate writing.
Despite some commonalities, each gospel has a differences in their telling of Jesus' story. In several cases, these tellings contradict one another (the day of Jesus' death being just one of more obvious examples).
So the canonical gospels, which cannot be proven to be eyewitness accounts and have no clear authorship, complete with contradictory details, cannot be reasonably taken for evidence for Jesus.
There are no known eyewitness accounts of Jesus' life and death. The closest thing that we have historical evidence for is Saul's (Paul's) vision of Jesus on the road to Damascus. Again, the is not to say that such eyewitness accounts might not be discovered someday, however that still means that we have no evidence now. Furthermore such accounts, once shown not to be forgeries, would only solve the historical Jesus problem, not the messianic Jesus problem.
Early Christian Writings
Many early christian writings, specifically those made by historians, are presented as evidence for historical Jesus. Some of these include the writings of Josephus, Tacticus, Justin Martyr, and others. Besides the obvious fact that none of these authors are contemporaries of Jesus, most of the non-contested passages simply make reference to christianity (many of the works that site Jesus directly have been shown to be forgeries or clerical "enhancements" made during the hand-copying process).
Having knowledge of a religious cult is not proof of the validity of its doctrine, only that it exists. This would be the equivalent of the some future generation using a journalist's report to conclude that David Koresh was the messiah. Therefore, even the historical documents that we do have do not make a strong case for the existence of Jesus.
As alluded to in the previous sections, there are no known contemporary references to Jesus. Even if one were to argue that there would have been no reason to have such references, that would not change the fact that we don't have any. Therefore, no evidence from this area either.
Old Testament Prophecy
I've seen several argument made that Jesus must be the messiah because he meets the qualifications set forth by the prophecies of the OT. Despite the fact that some passages of the bible contradict this argument (Jesus as Isiah) or create logical problems (Jesus comes from the line of David even though he has no biological father), some people still point to this claim as support for their argument.
Paul claims to have been a Pharisee, therefore he would have had working knowledge of OT prophecy. Considering that he's our only "eyewitness" and christianity's first evangelist, it seems pretty obvious that if he wanted to create a cult based on the messiah, all he would have to do is write a story about a guy that meets the conditions of the prophecies and presto...instant messiah. The fact that Paul's fictitious story corroborates key points from the OT's fictitious prophecies is not impressive nor is it convincing.
Revelation is the claim that Jesus is real because it has been revealed to someone. Usually this revelation is spiritual in nature, however sometimes there is a physical manifestation. The physical manifestations can usually be dismissed quite readily as mental illness, tricks of light, mass hysteria, or the mathematical probability that some potato chips are just going to bear quasi-accurate resemblances to outlines of cultural icons.
The spiritual revelations might appear to be a harder nut to crack until you consider that people have such "revelations" regardless of culture or era...and most of them have had nothing to do with Jesus. If a christian goes into a cave and meditates/prays for 10 days, he or she is going to claim to have had spiritual contact with Jesus. If a muslim does this, they will claim to have had spiritual contact with allah. If a buddhist does this, they will claim to have spiritual contact with....well, themselves, but you get the point. The only common thread here is that deep introspection causes most humans to have deeply spiritual experiences. To claim that one's own religion is the only one that can do this is to ignore the evidence. To claim that such an experience is proof of their respective deity is foolish.
Experiments using MRI technology have shown that there are "spiritual centers" in our brain. They are active when test subjects pray or meditate. They are also active in atheletes when they "go into The Zone". All these experiments show is that our brain and achieve higher states of consciousness. This is not a christian-specific phenomena.
Therefore, as with all the other examples provided, "revelation" is not evidence for Jesus.
The Story of Jesus is Not Unique
At this point, some might be wondering "well then, where did the story of Jesus come from?".
This is a good question and luckily one that has an answer. Remember that the christian myth takes part during the Roman Empire. The Romans (proper) were pagans that pretty much stole Greek mythology and changed all the names. The stories of Zeus and Jupiter are largely similar, except the names have changed. Hermes is Mercury, Aphrodite is Venus, Poseidon is Neptune, the list goes on and on. To summarize, during the time that christianity is developing, there are a myriad of pagan mythologies available but one of the most prevalent was Greek/Roman myth (keep in mind that christianity is an spin-off of judaism, which itself is one of many religions and not even a very big one at the time).
So what are the components of Jesus' story that really make him special. I believe the following list is representative:
* The Virgin Birth/Son of God
The Virgin Birth/Son of God
Ok, this may be the only item in this list that is arguable unique to christianity. However, ignoring the debate of the translation, the fact remains that there are several myths of gods impregnating women. Some of the more well-known Greek heroes resulting from zeus consorting with a mortal woman include:
There are at least a dozen more myths of about the children that mortal women bore for zeus. And this is just one of the many Greek gods that consorted with mortal women. And this is just one set of myths amongst a myriad of others.
So the idea that a god made a child with a mortal woman is hardly news. In the ancient world, kings and rulers were frequently considered to be the offspring of the gods. Jesus is merely a drop in the ocean of demi-gods.
Again, stories about miracle workers are nothing special. All religions contain stories of miracles, and while christianity is no exception, neither is it groundbreaking or unique in this regard.
I grouped death and sacrifice together because I wanted to limit myself to myths where the hero's death was a sacrificial one.
* Prometheus - son of Zeus. Stole fire from the gods so that mankind could learn and prosper (tree of knowledge anyone?). Zeus punished his son by having him shackled to the side of mountain, where a giant eagle eats his insides every day and his body is magically renewed every night. Prometheus sacrifices for all mankind.
* Dionysus - son of Zeus. Was fed to the titans as a sacrifice (sacrament?). Zeus slew the titans and from their ashes created mankind. Dionysus sacrifices for all mankind.
Here we have just two examples from one religion where the son of a god is sacrificed for mankind.
This is another all-too-common theme is mythology. The aforementiond renewal of Prometheus is one example. Hercules mortal body was shed when he died, however his divine spirit returned to be with his father in olympus. Adonis was killed and then brought back to life by Aphrodite.
I'm sure that someone will want to point out that none of these myths match the Jesus myth precisely. To them I would want to point out that no one is going to be compelled to accept a story that sounds exactly like the story they already have. Authors, novelists, playwrights, screenwriters, poets, etc are constantly making variations on a theme in an effort to pass their work of as "new" or "innovative". The early christian writers were exactly the same as our modern writers. They wrote stories that their audiences would accept and enjoy. No surprise that the stories aren't exact duplicates. I think the similarities are much more telling than the differences.
To summarize: The burden of proof is on christians to show that their belief system is true. I've summarized each of the areas where we currently lack any evidence for Jesus' existence, let alone divinity. Finally, I've shown the story of Jesus is not unique or special by comparing it to just one contemporary pagan religion.
I welcome any and all comments, arguments, contrary evidence, etc.
Thanks for reading.