Obviously, many lab chemicals are toxic, they aren't being used to hurt humans, hopefully, but could be. Reactive chemicals are quite useful, and they react with things like people adversely. It's sort of interesting to me they are classified as a weapon unless used for "useful purposes". So, as soon as I take some chemical and employ it to harm a person, I have weaponized it?
That strikes me as overly broad, but there it is. Literally.