I wouldn't say they would use them against us. But everyone know nuclear warfare is pretty risky. It involves more risks than benefits in todays era and there are more efficient ways to handle the situation.
We shouldn't rush into Syria based on an assumption. I am more worried about ISIS getting nuclear weapons (maybe Obama will give them some ;p).
It's really complicated to deal with this situation, but considering that no one really want to take a position there, I guess that with nuclear someone will have to.
Syria is certainly a country going through a lot of turmoil. To be honest Assad, as horrible as he is, is probably a lot less horrible than some of the other people who would come to power should he be removed or assasinated. The mistake we've made in the Middle East is that our leader have seemed to be pushing regime change regardless of the consequences. Sometimes the devil you know is better than the devil that you don't know. And that's clearly the case here.