At the same time, anyone who's taken Philosophy 101 understands that there's a real problem here. Hypotheticals can be sliced and diced a hundred different ways, and once you answer the first one you're going to get a second one sliced slightly differently and then a third and a fourth. And before long you're holding a freshman bull session on U.S. nuclear policy and which groups/regions/bad guys you might or might not be willing to nuke all based on questions that are deliberately designed to have hidden subtleties. And let's be honest: that's just not a good idea.
There's nothing wrong with Obama taking nukes off the table in a situation where, pretty obviously, nobody thinks nukes are a good idea. And sure, Clinton's and Edwards's criticisms of Obama on this score are mostly opportunistic. That's big league politics for you. That said, there's a genie here that, in general, is probably best left in the bottle. Speaking for myself, I'd just as soon the candidates shut their yaps about nukes unless they have a major and well-considered change in the U.S. nuclear posture that they want to propose. No bull sessions, please.
BY THE WAY: Don't forget that Obama recognizes all this too. That's why after originally getting caught off guard on the Pakistan nuke question and stammering his way through an answer, he immediately backtracked and said "Let me scratch all that." He understands the issue here as well as anybody.