Nuclear fallout is the major concern. Say you nuke a terrorist camp in Syria. The fallout would affect a much larger area than the initial destructive force, killing a lot of innocent people.
You could also argue that Syria (or whatever country) has an obligation to control terrorist activities within their borders, and by not doing so, they invite attack.
There's a lot of philosophy involved here, and the reprecussions of a pre-emptive or even post-emptive nuclear strike by the United States on what would likely be a 3rd world country that cannot defend itself are likely to be very steep. It would also likely trigger another nuclear arms race. In any case, I don't think I'm qualified to make the call on right and wrong in this situation.
Carpet bombing with MOAB's and bunker busters would hopefully get the job done and prevent any major international rallying against us. Besides, a really good bluff is just about as good as a good hand anyway.
