If it came to using mustard gas, I think the jury (if it came to that) would understand firearms more in your favor (in the US anyway).

Self-defense is always potentially TWO fights - the one you hope to survive and the one in court afterwards.

Trouble is, every perpetrator is "a good boy who was just about to get his life straightened out" when described in court. Using chemical weapons outlawed for war since WWI against the little angel doesn't look good.

(Even though I heartily agree with the concept!)