On the subject of Israel, we're all aware they were dropping chemical weapons on Gaza between 2008 and 2009, yes? That they lied about it to the UN, right up until one the shells hit the UN headquarters in Gaza, killing hundreds? If chemical weapons are such a 'red line', and the impending military action in Syria is all about the humanitarian effort to prevent further use of chemical weapons, where was the military action against Israel then? Interesting that when a business partner uses chemical weapons against citizens within its own borders they get a wag of the finger, whereas when an obstruction is alleged to have done it, bombing the fuck out of them is the only moral thing to do.
If you're talking about White Phosphorous, let me preface by saying I object to its use as an incendiary, which is the form in which it causes the horrible things it does.
With that said, saying WP is a chemical weapon is a bit disingenuous. It's not used in the way actual contemporary chemical weapons are and does not share the same traits. That's why it doesn't fall under the Chemical Weapons Charter and isn't legally defined as a chemical weapon(instead, in its' incendiary form it's regulated under the Geneva convention among other international treaties). So I'd say its the combination of less stringent, technically(of course not ethically) legally defensible status along with the US's cozy relationship with Israel that are to blame for why Israel didn't suffer any repercussions, not that they "got away with using chemical weapons"(because they didn't). Don't get me wrong, I think the usage is wrong and they should held accountable, but striking a parallel between that WP usage and the Ghouta attack is a stretch.