I think there are three compelling reasons to believe that male lethality is a phenomenon of biology:

1. It's cross-cultural meaning it persists even when you adjust for culture
2. It's the same for our closest animal relatives
3. It persists in the face of counter-conditioning. As a society, we spent no time or energy telling women not to be violent and an ENORMOUS amount of time and energy trying to stop men from being violent. Yet most murders and suicides are still done by men