This last question is something that I feel was addressed adequately at Alethian Worldview.
...In the first place, unless adoption or premarital sex is involved, there’s going to be at least some portion of the marriage in which there are no children present to be raised. And then they grow up and leave home, so they’re not part of the child-rearing environment anyway. So does the couple still have a marriage? ... Again, you’ve got a definition of marriage that tries to divert attention away from the relationship between the people getting married, and onto some contrived and disingenuous criterion intended to deny equal rights to a certain segment of society. Bad definition.That last bit is for those who want to "define" marriage. Interestingly (not really), their reasons for marriage being between a man and a women end up redefining their own definition. That's how bad the argument is. Still, I get quite insulted by these people who suggest marriage is about raising children. What about love? And the argument encounters other problems: Besides people who are intersex or infertile, what about elderly people who marry past their child-bearing years? (Well, I guess that technically makes them infertile, but most people probably don't view it that way.) And, more disturbing, what about teenagers? Is it OK for them to get married as soon as they can start reproducing? Why not? Remember, any reason given for this must be applied to everyone.
...And did you notice? Changing the definition of marriage so that it refers primarily to child-rearing is, ta-da, changing the definition of marriage...
And, finally, there is the pastor in the video below who inspired the title of this post. He's still essentially trying to make the same argument. Except that he seems to think that homosexuals are never born from heterosexuals. So he's got to separate the men from the women to ensure they don't reproduce for the sake of reproduction. Once again, the same argument can be applied to people who are intersex or infertile. So to limit the rights of one of these groups and not the others is discriminatory, plain and simple.
* I was discussing recently with Amy that it surprises me that the topic of intersex people does not come up seemingly at all in the discussion of gay rights, especially as a counter to these naturalistic arguments. I suppose intersex people are more rare than homosexuals and, from my experience, it seems intersex people tend to not talk much about their condition, leading to people being unaware that they know an intersex person. So this could create an "out of sight, out of mind" problem.