You call mating behavior and historical cross cultural and religious customs 'common practice'? Yes. However, most common practices are not opinion. They are exactly such because they are true.<quoted text>
He doesn't argue with you because you don't present an argument. Your assertion is an appeal to common practice--that same-sex marriage is not marriage. And since common practice is based on opinion, not on truth or fact, it is a false argument.
I keep asking if you read what you write, you really should. I think you'd laugh too.