Marriage is a holy union between a man and a woman, and it compliments God's command to "be fruitful and multiply". Marriage, as we know it in an Earthly sense, also mirrors a Christian's spiritual relationship with Jesus. IOW, it mirrors the spiritual marriage between Jesus Christ and The Church.
In a secular frame of mind, marriage is a union between a man and a woman, IOW, a union in which procreation in principle is possible. This possibility of reproduction (being fruitful) is what gives marriage its meaning. Without that, we are only left with a close fellowship between two people.
Gays, in this manner, bastardize marriage via their feeble attempt to make their relationship into a sexual one, even though reproduction is not possible (even in principle) since a butthole is not a vagina (and a vagina is not a penis). A "gay marriage", while not platonic in the minds of the two participants, is ultimately no different in result than a platonic relationship between two people.
There is absolutely zero possibility for reproduction in a "gay marriage", not even in principle. This renders the whole notion of "gay marriage" to be completely and utterly meaningless, and in no way is it the same thing as a marriage (in which reproduction is possible, even if that possibility only be in principle).