Note that there's quite a difference between legal (secular) marriage and the Christian concept of marriage.
Nobody (as far as I know) is advocating that any religious institution perform ceremonies for marriages that are contrary to their doctrines. Rather, it is about legal recognition of such marriages.
Nobody (as far as I know) is advocating that any religious institution perform ceremonies for marriages that are contrary to their doctrines. Rather, it is about legal recognition of such marriages.