Coming from a Biblical and consistent Christian perspective on marriage, rejecting the damnable compromises embraced by the liberal denominations claiming some vague connection to Christianity whereby they have deliberately chosen to reject the word of God while claiming to believe some of it (those parts that fit conveniently with their man-centered theology), I see same-sex marriage as being an affront to the holiness of God, the word of God, the God-ordained plan for marriage, and His church in several ways, two of which I will address here.
First, homosexuality is one of the behaviors/lifestyles practiced by those who "will not inherit the kingdom of God" (Roms. 1:18-32; 1 Cor. 6:9-10). The homosexual lifestyle/practice is by no means the only lifestyle that betrays an unregenerate soul (see the others named in the above Scripture references). But it is the lifestyle that demands and receives attention from the media, the government, and the church. And it is for this reason that it is kept before the general public; this attention is much wanted by the so-called "gay community." The old proverb is true, "the squeaking wheel gets the grease."
Why? Why do homosexuals want this attention? Well, by garnering all this attention they have played the media as they wished, using it to be portrayed as both victim and hero and in order to sell the idea that homosexuality is an accepted lifestyle by our culture. The suffering homosexual and the cutesy homosexual of Hollywood have both endeared themselves to the wimpy American public conditioned by decades of feminism and weeping males who can't look in their own refrigerators without their wives scolding them.
Under the "old covenant" initiated by God between Himself and the Hebrews, homosexuality was described as an "abomination." (Lev. 19:22; 20:13). However, it is never described as such in the New Covenant. Mind you, however, it is clearly one of many practices that indicate that the one practicing it will be finally damned on the Day of Judgment. For many, the day of judgment has already come, God has already turned them over and given them up in the present because of their insistance on living as they want, refusing to repent and believe the gospel. (Roms. 1:18-28)
Second, same-sex marriage can only be called "marriage" by those who have deliberately rejected the clear mandate given by God that marriage is to be between one man and one woman (Genesis 1:26-27; 2:24). This is what God "has joined together" (Mt. 19:1-6). Same-sex marriage "separates" or "tears asunder" what God has joined together by the joining together of a man with a man or a woman with another woman. Same-sex marriage violates the God-ordained act of marriage by joining together what God has forbade. Whatever it may be called, it cannot be called a marriage.
I mentioned earlier that homosexuality is never referred to in the New Testament as it was in the Old Testament (covenant) as an "abomination." I also pointed out, however, that their are practices that inform those who observe them and those who do those things that those practitioners will not inherit the kingdom of God. But that is not the final say. 1 Cor. 6:9-10 gives a partial list of those who will not inherit the kingdom of God ... except they repent. But v.11 in that same passage says this, "And such were some of you. But you were washed, but you were sanctified, but you were justified in the name of the Lord Jesus and by the Spirit of our God." And I will close with the warning that Paul gave the Corinthians, "Do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived." Become one of those washed, sanctified and justified by the grace of God by believing in the One who did for us what we could not do for ourselves.