I don't think anyone should use thermobaric weapons (or really any weapons, at least offensively). But can someone explain what "banning" them would do in an in

I don't think anyone should use thermobaric weapons (or really any weapons, at least offensively). But can someone explain what "banning" them would do in an instance like this? Can we ban nuclear weapons too? It seems to be consensus that the war is illegal, what does making any of the actions more illegal do? It's the geopolitical equivalent of writing new laws about things that were already illegal under old laws, to give a sense of doing something, without doing something.