Most criminals are kind of stupid though - at least the ones who commit crimes that don’t involve some form of financial gain. Note: this is the belief among criminals themselves.

I mean the convergence of beliefs across a bunch of religions and moral philosophies is probably pretty good evidence. They were not exactly running randomized controlled trials; but they were smart people who thought a lot about this stuff. I’m not sure that the methods of modern behavioral science are so much more advanced :)

Otherwise this is just like one of those “obvious”, self evident things (i.e. obvious to some not to others). I do concede that there are a subset of jerks who have Dunning Kruger syndrome as well as a small number of true sociopaths out there.