There is nothing "Christian" about marriage, Sassy, it is contract between two people. Its original purpose was to protect the ownership of property by controlling the sexual behaviour of women.
Religion (ie the organised, large scale, control of the behaviour of other people by using fairy tales) became involved when it was realised that strongly associating "shame" and "guilt" with sex was a very powerful method of control.
If two men choose to marry, or if two women choose to marry, then let them. What other people choose to do with the contents of their underwear is none of your business.