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.
Scroll down to section 3.a.ii (or ctrl+f search for "Implication: monogamous marriage reduces the spousal age gap, gender inequality and fertility")
Anecdotally, this is what a family friend who worked as a counselor for Southern Utah University observed repeatedly. SUU is located in Cedar City, which has one of the highest concentrations of present-day polygamists in the US.
EDIT: added source; had previously assumed this was common knowledge