I'm not sure how the U.S. should proceed with respect to the uprising in Syria, but I think the claim, on the basis of no evidence whatsoever, that those battling the Assad regime are democrats needs to be subjected to scrutiny. (See this, for example, which equates American reluctance to overthrow Assad with a reluctance to promote democracy, as if the two things are in anyway related.)
There is absolutely no reason to believe that Syria's rebel forces will be any less brutal than the regime they are seeking to overthrow. There is no way to know how they will govern (and there is obviously no reason to trust declarations made explicitly to court foreign assistance). Nor is there any way U.S. or NATO assistance can ensure a democratic outcome. The U.S. couldn't steer Iraqi politics to its liking while it was an occupying power - it would have even less leverage in a post-Assad Syria.
None of this is to say that a democratic Syria is impossible or that those risking their lives against the Assad regime do not genuinely desire a more representative government. It's also not to suggest that there are no good reasons to intervene (in some fashion) in Syria's uprising. But for the case to be made with a modicum of intellectual honesty, it has to acknowledge that the nature of a post-Assad regime is absolutely unknowable and could produce human carnage far in excess of anything we're currently witnessing.