If he was asked why he agreed with one deviant behavior but not the others, I'm sure he would have a readily available explanation. (sarcasm alert) As of now, he supports Gay Marriage because his Son “loves” another Man.
Taking the position he just announced is based on the notion that such behavior is a Civil Right, which if accepted ingrains the behavior into Society as a norm. Well, people who want to be Polygamists or want to Marry their own Blood Relatives would tell you the same thing. The entire concept of Gay Marriage fails simply because those who accept it must also accept every deviant behavior or deny the same “Civil Rights” of those choosing to be involved in them.
Homosexuals are being carefully trained in their mind bending of society. They have gay clubs in the highschools so that they can feel comfortable in their milieu. They are trained in how to “come out” to their parents and what sort of language to use. I believe they probably lean more heavily on the mother as being the one who’s motherly portective instincts will be more easy to exploit. So mom works on dad and dad finally caves in. I think that is how it probably worked with Portman and in most homes.