I have to agree with Jae - lying is a very specific verb. The example that you mentioned - a person who offers a counter-opinion without immediately explaining how they formed that opinion isn't lying. You can question the value of their argument, but you can't accuse them of lying. Also, sometimes the explanation a person offers for their opinion simply doesn't satisfy our own requirements, in which case you either ask that person to clarify the confusing part, or you simply agree to disagree.
Now, when it comes to the main question of this thread - sanctions for lying and to which extent should they go (if at all) - I think it depends on the nature of the lie.
For example, (this actually happened very recently on another forum) a member posts art in the art section of the forum, but he lies about him being the author of said art. Other members who have already seen said art somewhere on the net begin to suspect something, some outright accuse him, others ask in a more refined manner about some details, others find actual evidence that the art isn't his and provide links. In the end the thread is locked and deleted and the offending member was (as far as I know) punished (most likely banned, but I can't say for certain). Now, while this isn't the best way for members to behave (I personally think it would have been more civilized to report the thread to a mod and present evidence directly to them, instead posting them in said thread), the infraction was handled (and it definitely should have been handled) and the offending member got even more than he deserved - he was exposed in his own thread, which undoubtedly caused some humiliation and hopefully that person won't repeat the deed again.
In conclusion, yeah, some forms of lying should be sanctioned, but the trick is in recognizing them.