here he is talking about a father marrying a son
http://www.dlisted.com/2013/04/03/i-cant-files-jeremy-irons-thoughts-gay-marriage
btw, there are a lot of libs with lots of money that might be looking into whether they can marry their sons to get rid of death duties now that someone came up with the idea.
Jeremy: It's not incest between men. Incest is there to protect us against inbreeding, but men don't breed, so incest wouldn't cover that. Now if that was so, then if I wanted to pass on my estate without death duties, I could marry my son and pass on my estate to him.
Josh: No, that sounds like a total red herring. I'm sure that incest law would still cover same-sex marriages.
Jeremy: Really, why?
Josh: Because I don't think that incest law is only justified on the basis of the consequences of procreation. I think there's also a moral approbation that's associated with incest.
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And not so long ago, there was also a moral approbation that was associated with homosexuality...