Sound the Rape Culture alarm! Ring the sexist bell! I can’t get past this line until something has sounded. I mean – possibly Hamlet is meaning that Ophelia specifically makes monsters of wise men but that’d be a lot for one mild mannered pretty girl to do. It seems a lot more likely that this is one of those “women turn men into monsters” situations. See, baby, you made me rape you with that pretty face. See, you made me a monster with your beauty, pretty girl. See, I’m not responsible for my actions because you showed up and disrupted my flow.
I don’t think wise men know what monsters women make men turn into. I think wise men know that respect and responsibility are a whole lot more wise than throwing up ones hands and saying, “I’m a monster! That girl made me do it!”
Wise men say, “If I am a monster, it is a monster of my own making. And while any number of factors may have encouraged my monster making, I always had a choice.”
The Hamlet Project 
Monsters in this context refers to cuckoldry. He’s saying that wise men will not marry her because they know that she will be unfaithful.