I'm aware not all women say this, but I hear it enough: women complaining that other men often don't step up to defend them from something other man is being uncomfortable to her, even if the innocent guy has nothing to do with that woman... as if risking your own life would be preferible to her inconvenience.

Truth is that men don't have much power about what other men do or pick or fuck, and proof of this is that if men did have that power, they would indeed use it to stop sexual competition. It is also a thankless job, as the many men beaten for trying to defend a woman from her dangerous boyfriend, for her to just go back to the evil boyfriend and the poor guy left there to bleed.

Men may not hold other men accountable in any significant way, but women can pick better men, and fortunately most men are not dangerous. Most Women have way more options to pick men that men to pick women, especially if she is single and young and thin, but even if they are ugly they still have way more options than ugly men. 90% of men don't have many options to pick women unless they are genetically lucky.

TLDR: Since women have way more options dating, it makes sense to rather say that it is women's responsibility to pick better men, and not other men responsibility to enforce your arbitrary criteria or punishment on men you picked and now hate.