Leftists twist themselves in knots to get out of this argument, but
if “one man and one woman” is an “arbitrary” definition of marriage that is subject to revision,
how is “two adults” any less of an “arbitrary” definition?
Simple,
Gay marriage won’t hurt any traditional marriages. Nobody is going to say “Wait, I can marry somebody who’s the same sex as me! So long honey, have fun with the kids...”
Legalizing polygamy can hurt traditional marriage, if a husband or a wife would want to take another spouse and the current spouse refuses, the requesting spouse can file for divorce with cause and get a favorable alimony, custody and division of assets ruling.