It's not a weakness. It's an ingrained desire to protect the species. When a man is killed, it's "just" that man. When a woman is killed, it's her and her potential progeny.
It's an ingrained territorial imperative. Don't f*** with MY woman. Call it a strength if you want. But it is a fairly rigid position, I have it, and if you're a guy, I'll bet you have it too.