> or stop them from reproducing

It may not be possible to breed any trait to any distribution one would like.

For body size, maybe, also depending on maternal nutrition. But apparently there is (and anthropologists think always has been) a certain percentage of people with schizophrenia even though it carries a severe reproductive disadvantage.

Similarly, it may well be that personality always approaches a certain distribution like a random experiment.

The culling mechanism would work in any case, of course.