I'm not about to blog on this issue extensively; it's been well covered by other bloggers, especially Josh Marshall (latest entry here).
What I will mention is that this is going to throw the perceived hypocrisy of the democratic North (in the eyes of the rest of the world) into sharp relief. The core of the "we like Americans, but don't like their government" concept is that while the United States (among other states) considers democracy and human rights precious within its borders, it is perfectly willing to sacrifice them outside said borders to forward its interests. Hence the reason so many people loathe the United States' foreign policy at the same time as they're desperately trying to immigrate; they know that democratic ideals often lose out to raw realist "national interest" once you cross those lines.
This was always the dangerous part about using humanitarian arguments for justifying the intervention. They were always plausible, theoretically, as long as the United States could be seen as having its collective "heart in the right place", even while it was prone to mistakes caused by cultural ignorance. (Such as tromping around Mosques in army boots and the like). Even the horrible pictures and footage that show up on Al Jazeera could be explained away as "collateral damage" or tragic mistakes. These photos, obviously, are not tragic mistakes, and will be seen as systemic failures no matter how many cries of "isolated incident" rise up from those whose careers depend on people buying that argument.
Without that flimsy veneer, the humanitarian arguments are valueless, and at this point nothing else is left. Except maybe for the "removing a threat to Israel's security" bit, and having a huge unstable hole at the centre of the Middle East isn't in Israel's interest, any more than it is the United States'. Thus, the United States is left fighting a war without any real purpose, except trying to fend off the consequences of invading in the first place. Nobody is going to accept that, and the realities of trying to fight such a war is going to make the situation, if anything, worse than Vietnam.