Victors get to say what was a war crime and what isn't. As it stands many nations are trying to eliminate land mines or at least put a self destruct device in them. Napalm is now classified as a chemical weapon and Willy Pete is not labeled for use on humans- though the tongue in cheek answer is it was used on the enemy's web gear.
Most of the chemical weapons we think of- Mustard, phosgene, VX, and of late sarin are true horror weapons and their use in WWI lead to banning them as soon as practical. As a young man being trained to protect myself from the rather impressive varieties of chem weapons the Warsaw Pact had and the very feeble methods we had, no MOPP gear back them, sticky fatigues kept in a special wrapper and some sticks to scrape the crap off and a powder puff to neutralize the residue I am double D damn glad 'we' wised up and refrain from chem weapons.
As far as bringing them back... the 'we' who ponder that are not the 'we' who will face it.