I know from history men have lived with men in a homosexual relationship being not married. That is also true of women living in a sexual relationship with another woman. Christians if they are going to be true to the Bible have to say that homosexuality is a sin the same as adultery, idolatry, greed, the list of sins would be endless.
Now I know people who are not Christians and reject the Bible will do what they want to do meaning live contrary to the teachings of the Bible. These unconverted people will marry whoever they want regardless of what the Bible teaches. It always has been this way. I still think a Christian or Christians have the right to voice their views even if the unconverted think they are full of crap.
I do not think we can make people live moral lives by making laws. I do think though the Government has the duty to follow the teachings of the Bible when it comes to righteousness and justice. But once again I recognize the American Government is morally corrupt and will pass laws that are contrary to biblical morality. We read in the newspapers these days of the Government taking down monuments that have engraved on them the Moral Law/Ten Commandments. Once the US Government rejects God's Law we are ruled by the immoral majority. So as a Christian we must be grieved by all the lawlessness around us, but at the same time we know that is the way of the ungodly.
I do not know if a Government should give homosexuals legal rights. If a Government is totally given over to wickedness how can a Christian expect the Government to do what is biblically God honoring? If the majority of people have given themselves over to the lusts of the flesh they would want a Government that would make it legal for them to pursue the satisfaction of their corrupt lusts/live in a state of lawlessness. All a Christian can do in such a society is pray for the Second Coming of Christ and be salt and light where ever the Lord has planted him.
"It's Time to Legalize Polygamy"
http://www.politico.com/magazine/story/2015/06/gay-marriage-decision-polygamy-119469_full.html#.VZPALvlVikq
"After Gay Marriage, Why Not Polygamy?"
http://www.vice.com/read/after-gay-marriage-why-not-polygamy