No one is telling boys that they are monsters.
It is helpful that they know there are humans in the world who behave like monsters, and that some of them are men who target people who they perceive to be weaker than themselves.
So children, women, other men who are either physically smaller or in a lower position of power. That’s what they need to know. So they can protect themselves, and help stop others from becoming someone else’s monster if the opportunity arises.
Doing things like speaking out against sexual harassment, and calling out bullying behavior, this is everyone’s responsibility btw. Not just men’s and boys, but this is what needs to be taught so world can suck less.