Actually, I think the Muslim gentleman makes some good points. Religion can label things as sinful and still tolerate other people who commit "sins". That said, I'm not sure that the followers of Islam actually tolerate "sinners" very well.
Although I would say most people are really apathetic about homosexuality, there is something sinister about normalizing this alternative lifestyle. Once you put same sex relationships on the same level as heterosexual relationships, you are going to add confusion to children about sexuality that would otherwise not exist. In the end, you are trading the emotional well being of homosexual adults and their children, for the emotional well being of children who are trying to figure out their own place in the world and although it might make a safe space for those children who are homosexual, I can see how it would alienate those who are not.