I think it would be more fair to say he would discriminate based on perceived risk to himself. In this case, that risk is based on the sex of the person involved, but his argument can also include, for example, hiring someone with lesser qualifications, who is less likely to be promoted past him, over a more experienced candidate.

The more general point would be, be aware of the second order effects of changes you promote. For example, revocation of innocent-until-proven-guilty would almost certainly reduce the chances of people who have blown the whistle of being hired again, as they would present a much higher risk to prospective companies, regardless of whether their claims were true. The fact that they would blow the whistle at all would serve as a huge red flag.

Of course, I don't actually know the incidence of sexual harassment at workplaces, and have no idea whether false reports are even an issue. I strongly doubt they are, but I can somewhat understand male managers fear of them, given that they can ruin careers and marriages. As much as sexual harassment is a problem, I don't think assumption of guilt is an appropriate or long-term effective solution.

When you introduce irrational events into a mostly rational world (i.e. when you introduce "believe before investigation" into a world run by financial compensation) then you're bound to have irrational responses, such as discrimination, yes.

Assuming other people aren't psychopaths is irrational optimism, while desperate defensive strategies like not hiring high-risk people are perfectly rational.

In a world where no evidence is required before firing, then that would be the sane thing to do. Always hire the sex you are not attracted to and make your sexual preference very clear.