This has literally nothing to do with poly(gam|amor)y.

For one thing, looking for younger women / men is not wrong. As long as they're consenting, and old enough to consent.

Further, any relationship of any kind has the potential to be abusive. This is no ground to say it shouldn't be allowed. This is like the idiotic christian bigots that think homosexuals are bad because they're child molesters. No, they're not.