Patriarchy is a dominance based hierarchy, and men are always having to perform their masculinity (if they are bought in to this culture). Part of the performance is through bullying of anyone perceived to be weaker or lower down the hierarchy (women, gay men, someone of a different race or religion, etc.) It's a bad deal for pretty much everyone, even the guys who are doing this, because there's always a bigger dog somewhere.

Thanks for spelling it out so well how stupid and destructive this all is.