Just a quick note to throw out there, the phrase "Life, liberty and the pursuit of happiness" is actually from Jefferson's Declaration of Independance, not the US Constitution. It's supposedly based on John Locke's "Life, liberty and property."
Some use this to argue that the DOI is just a statement of philosophy, not law. Others take it to be that this is how the laws ought to be written Edit: (or interpreted), with this philosophy in mind (rather than saying "that's nice, but who cares").
It also comes down to what the role of the Constitution is. Is it a "living document" that must be changed based on the majority view of morality and governance at any given time in history, relying on the spirit of the times? Is it a sacrosanct piece of wisdom that will save us from ourselves? (and the desire to lapse into apathy and a comfortable dictatorship or the popular anarchy of mob rule?) It's an interesting aspect of the discussion anyway...