While the lead poisoning wouldn’t cause the toxic thinking, racism, and belief in conspiracy theories - it would have made them much more susceptible to it from those around them.

Like all good science, correlation does not imply causation. However, we do know that lead does accumulate in brain tissue, and we can see that the rise of lead in the atmosphere had a very strong correlation with violent crime, and the reduction of it reduced violent crime. This study and IQ show the relationship as well.