Chemical weapons

I don't get it.  Why is killing people with sarin gas any worse than killing them with bombs or guns or artillery?  From what I've read, just a tiny fraction of dead Syrians were lost to chemical weapons.  How did those come to be the "red line?"

My guess is that when a President of the USofA shoots off his mouth, he's kind of stuck putting our money where his mouth was — so now we'll be shipping unspecified weapons to unspecified SLA units, with no idea of where they'll finally find a home.  Best bet for final destination is the guys with the beards.

There are times you just can't win.  Like now.