I see this a little differently. I view same sex marriage/homosexuality in general as completely and utterly wrong given scriptural precedent in Old and New Testament, but I am not sure you can argue against it politically. Divorce is legal but lawyers carry it out apart from the church as well as the people who separate from either other. I just don’t want churches who believe homosexuality is wrong to be forced to marry homosexual couples or for our religious freedoms to be taken away. Churches are not businesses. They are private religious institutions so they should be able to follow their beliefs. All private organizations have some areas where they discriminate against people. Some don’t cater to special needs children. Others don’t cater to children. Some cater to Christians. Others to Hindus and so on. Private schools are another example. Businesses, like a bakery or hotel, on the other hand should serve to everyone if that is their general practice. If your hotel serves people who are acting on a one night stand but not a lesbian couple that is very wrong.
As far as polygamy, you see many men in the old testament had multiple wives including Abraham, Jacob, David the man after God’s own heart, and others. They were blessed by the Lord and God never denounced their polygamy. The only one who got in trouble was Solomon because God said for kings not to marry many women, especially not foreign women who could lead them astray. In various New Testament letters it says that elders and those in authority should not have multiple wives because they should hold to a higher standard of living. Elders are supposed to be the husbands of one wife but for the average man having several wives should be more accepted. I don’t think polygamy is wrong before God.