Honestly could be a little of column A, a little of column B. Or even the lead, like you mentioned. Lead is one of the leading theories for why there were so many serial killers, but it's also a theory on why the Baby Boomers are so much more conservative than the generations before and after them. Symptoms of long-term lead poisoning include things like heightened aggression, violent tendencies, and impaired cognitive abilities, and the theory also correlates the coincidence of serial killers largely disappearing in the time since lead was banned from gasoline, paint, pipes, etc. - but that also fits for the political stance of generations before and after the introduction and banning of leaded gasoline.

Obviously, there's more to it, but I can't say that I think banning the lead was a bad idea!