What evidence do you have for any of these claims? In particular, how do you know that stereotypes are on average exaggerated relative to the true conditional probabilities, or that they are slow to update in changing circumstances?
...Common sense?
I really didn't think it would be something I'd need to prove.
Evaluate various stereotypes about ethnical, religious, political or really other social groups you've heard. How many of them are objective? How many of them are accurate? How many of such generalizing statements are made about groups so diverse that you really cannot say much about them in general? And finally, how many of these groups have you personally interacted with enough to authoritatively evaluate those opinions?
The article to which I linked lists a few stereotypes that seem clearly true to me, and any reasonable person would readily act on them. (Would you really get equally scared of old ladies and young men when walking in a bad neighborhood?) So how exactly does your common sense alone let you sort out true stereotypes from false ones, and to conclude that most stereotypes (by whatever measure) fall into the latter category?
Moreover, if you believe that acting on some kinds of stereotypes is unethical, that's a defensible position which I'm not going to dispu...
There was a historical shift in beliefs.
I find this very odd. How could a major cultural lineage be wrong about something so much a part of ordinary experience?
When I say wrong, I don't necessarily mean that we're right, or the ancients were right, though there's a lot of evidence that the Victorians were wrong.
My favorite theory is that people's amount of desire for sex varies sufficiently that there's enough noise to make it easy to see patterns that aren't there. I leave the possibility open that there was a change (possibly dietary) which affected libido levels differently between men and women.
People are sufficiently punitive about sex that there's going to be lies and misdirection to support the current theory about how people are supposed to be.