Jeremy Irons Thinks Gay Marriage Will Lead To More Incest

I'm not exactly sure how gay marriage has anything to do with incest, but somehow, Jeremy Irons has attempted to link the two and said in an interview that  same sex marriage could lead to incest between fathers and sons, fearing it will "debase" marital law. Huh? So, lets say that two women decide to get married. A father and son hear about this and then decide the world is coming to an end and end up having sex? His remark is so strange that gay and lesbian groups had no idea how to comment except to call them bizarre. If you are a gay rights group, you really don't want to respond because you will be saying something like, "Gay marriage will not lead to more father/son incest." Do you really want those in the same sentence for a Google search? Was there a lot of father/son incest previously? Maybe there was none previously and someone found one case and they blamed it on gay marriage? I guess it does not affect the mother/daughter incest rate?