Paedophilia had thrived largely unchallenged for millennia – indeed, for much of history girls married at about age 13. But with the equal relationship as new ideal, paedophilia has become indisputably taboo. ...The article also cites data saying that many more people disapprove of adultery now than did 40 years ago. They argue that a "wink wink nudge nudge" in the days of unequal marriages tacitly approved of men seeking discrete sex outside marriage, but now, the legacy of the 60s is that equal partners deserve equal commitment.
Another unequal relationship, prostitution, is in trouble too. ...
Even unequal marriages are under attack. Once upon a time, when a rich older man married a young woman, they might both have expected congratulations from friends. Now they can expect mockery.
This agrees with the writings by marriage scholar Stephanie Coontz that the real "redefinition" of marriage came when we de-genderized unequal relationships and made husbands and wives equal (see our discussions of her research here and here).
So, marriage equality is a force for GOOD.