You're reading too much into this, I think. Bad kids do exist. Be compassionate, but do not encourage involvement with them.

I have really really profound regrets about not doing this myself, with my kids.

exactly. unconscious bias is an observed psychologic phenomena and i have my doubts if an adult can opinate agnostically about all of them. sure you don't want your kids getting together with bullies but that's basic compassion. let them tie/explore with people freely