Why did people start thinking women are the stronger sex?

I've started seeing this in the internet a lot. They believe the male groin is so weak that the actual stronger sex is women, and if a woman and man were the same size she'd win every fight. I just don't get why people think this way. If that were true i don't think violence against women would be an issue, and rape wouldn't happen this much. We certainly would not have patriarchy either. Why do people keep pushing this belief and agenda about female superiority? Also, here's a poll.

They are wrong, men are stronger
They are right, women are stronger
Select gender and age to cast your vote:
Why did people start thinking women are the stronger sex?
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