Say what you (or Kubrick) will about mutually assured destruction, it sure does seem to have prevented a lot of violence, despite also seeming totally insane.
Europe, for sure is a lot less violent, as for the rest of the world? I won't believe that on face value; south America specifically got more violent, and I suspect everywhere else is a wash (or is not attributable to American force projection). I attribute the peace in Europe to the EU rather than pax Americana.
Overall violent death is down on planet Earth drastically over time.
But I’m with you, on balance wmds are terrible things. One use of them could outweigh all the violence they prevented.