In armed conflict, dead is dead. Killed by a bullet. Or a cluster bomb. Or gas. Or napalm. If hit by a bullet, it might be mercifully quick: but it might be very slow and painful. Or maybe not even death, “just” a permanent disablement, leaving you seriously crippled, wishing you were dead. Ditto for gas. Or a cluster bomb. So… dead is dead… why do we differentiate between chemical weapons and other weapons? ALL of them are dreadful.
My theory of the ban on chemical weapons is that chemical weapons are cheap and much too easy to acquire, and would empower small weak countries. And not in the interests of the big guys.