Why does chemical weapons matter more than any number of horrible ways people are killed by their governments? And how does it change that we will ultimately fail in setting up a stable ME government for its victims?
Well, for starters, they aren't localized nearly as much as conventional weapons. Their effects are tantamount to torture, and it is unavoidable that large populations of civilians will be affected by them, no matter how carefully they are aimed. I mean, not even the nazis used them ... actually no one did during WWII because of how devastating their effects were in WWI.
I think they should be off limits no matter what. And, Assad is not just using chemical weapons, he is using them against civilians. When we drop bombs, we do what we can to minimize civilian casualties. There are, obviously, unavoidable civilian casualties, but the point is that they are avoided as best we can. The use of chemical weapons means that civilian casualties are not being avoided at all.
In regards to leaving them leaderless, I'm not sure what you mean by that. We didn't assassinate Assad. He is still alive and kicking. We just sent him a message that the use of chemical weapons will have consequences militarily.