We have international treaties that ban biological and chemical weapons. Other weapons that are regulated include anti-personnel mines, cluster bombs, and blinding lasers. Expanding bullets are banned in military uses as are incendiary weapons against civilian targets.
That's the state today. Throughout history there's been a long negotiation about what weapons have been allowed in combat.
tell that to the people that Assad gassed -- in his own country -- or the Kurds gassed by Saddam. Or all of the chemical weapons used in the 1980s during Iran-Iraq.
or all of the people dying from AP mines in Ukraine.
half the world signed anti-mine treaties because they knew that if the real shooting started the US or USSR (who didn't sign the treaties) had a stockpile to send them.
there are easily searchable videos of the incendiary weapons being used against Ukrainians.
the only reason we dont have antimatter weapons or gravity guns is because we haven't figured out how.