I agree with him that same-sex couples must not be allowed to adopt under any circumstances, and that marriage among them simply does not exist. He has a point in saying that there are many other kinds of relations like plural marriages or incest, so what's the point of registering just gay couples?
But I strongly disagree with him in that he mentions polygamy in a despective way and compares it with incest, and that he says marriage is for life. I find it strongly offensive to the Patriarchs who did in fact practise polygamy and also got divorced. Abraham had two wives and divorced Hagar. Irseal had four wives. In fact, Judaism does not consider polygamy to be wrong. It's only forbidden now by Ravs for practical reasons.
As I said in another post, I find it wrong for Jews and Noahides to side with right or left wing non-Noahide parties. Jews and Noahides are a minority everywhere (except for Jews in Israel), if right wing Gentiles can claim the numbers argument to ban something, how can we know if some day they will not turn against Judaism also?
By this I am not saying that it's wrong to accept the support of individuals, I am only saying that it's not wise to side with parties or groups which may have their own agenda, and even if their leaders were sincere, we never know where their movements can be lead to by the masses.