Well, of course, it's another day in the fight to justify as much sin as we can get away with, so the internet is all ablaze with people who don't know their moral left hand from their right. One of the tired arguments from supposed Christians who support gay marriage is that we shouldn't judge others simply because their sins are different from ours. But does this objection really hold much water?
First, saying that we shouldn't judge others for their sins, because we have sin ourselves, runs counter to the biblical witness that tells us we are, in fact, to judge others for their sins if they claim to be Christians. First Corinthians 5-6 makes it clear that all Christians fall under the jurisdiction of the Church and that any church that does not deal with a person in willful, unrepentant sin, is itself under the judgment of God and needs to repent itself.
Second, it assumes that all sins are equal, which, of course, they are not. If all sins were equal then there would be no possibility for the Lord to tell the Pharisees that they would undergo a "greater condemnation," or speak of some receiving few lashes as opposed to others receiving many, or speaking of judgment being more tolerable for Sodom and Gomorrah than for those who reject Christ after the witness of the Spirit has been given to them. Sins are different, and that's why punishments in the law are not all the same either. Some broken laws require temporary or permanent exile, some require a fine, and some require death.
Third, and this is the really important one, homosexuality isn't just another sin that may bring one to judgment. It is the first sign, the revelation of God's wrath, that judgment has come upon that particular person or people. Romans 1:26-32 states that this is something to which God gives people over as a wrathful judgment against them. It means that God is angry with them, not favorable and a.o.k. with what they're doing. This judgment itself is a result of people distorting God's holiness/otherness and making Him more like themselves or something even lesser than themselves that they can manipulate and control. In other words, it is a result of people making God accommodating toward their sins. He is not the God who judges, but the God who can be controlled by His finitude, as creation can be controlled. We do it today by holding God's holiness at bay by saying He is a God of love. So we reduce God to a single attribute and then redefine His love as "acceptance," a definition of love that allows for us to use His grace as a license to sin without consequence.
But homosexuality isn't the only sign of this judgment. It is a form of the larger sin of sexual immorality, because sexual immorality itself is a use of sex that is non-procreative. The judgment here is the same as in the OT, where God cuts off one's offspring in His wrath and judgment. He blots out the person from the earth by making him the last in his line. What we see here is a merism in Rom 1:26-27, where men are engaging in unproductive sexual acts with women and contrasting that with men committing unproductive sexual acts with one another. The full range of sexual immorality then is meant in the allusion (i.e., any unproductive sexual act with other humans). Hence, it is not merely the homosexual who is under the judgment of God, but any who practice sexual acts that are not according to the creative order God has put in place for His images to practice.
Now, here is the thing. The question isn't whether some are under the wrath of God and others are not, but whether a Christian should be one who moves out of the wrath of God and into the grace that has been given to him so as to no longer participate in sexual immorality/non-procreative sexual acts. Romans 2:1 indicates that both Jew and Gentile (i.e., everyone) is under the wrath of God and that their sexual misuse is a sign of this. What is a sign of one's acceptance by God, however, is the gospel that now calls him to correct his distortions of God and his distortions of his anticreational actions.
Hence, out of all of the sins from which Christians are commanded to abstain, sexual immorality is essential (cf. Acts 21:25; Rom 6; 12:1-2; 1 Cor 5-6; 2 Cor 12:21; Gal 5:19-24; Eph 5:3-12; Col 3:5-7; 1 Thes 4:3-8; and Jude). This is true because we are to be moving out from our former roles as anticreational agents of chaos that worked against God's purposes of good in the world and toward our creational roles as His images as we do all manner of good in service of the true and living God (as opposed to our made-up version of God that once accommodated our sin).
What this means is that the person who is moving away from sexual immorality is the person who has become acceptable to God through Christ and His work; but the person moving toward justifying and indulging in his sexual immorality evidences his rejection by God and that he is still under God's wrath.
So how should we perceive things like gay "marriage"? Well, the person obviously is not struggling with his or her sin any longer. He or she has fully accepted it as acceptable to God. Hence, this person has never been saved. He or she is still under the judgment of God.
The person struggling with sin is another story. He or she may desire now to live as a Christian according to God's holiness, but is often defeated. This person needs mercy and grace and our help in his or her plight to move away from what is evil.
And what of the heterosexual person supporting gay marriage who also claims to be a Christian? The Scripture indicates that those who help others move into sin by justifying it are partakers of that sin, and hence, we must conclude that they are also partakers of the judgment of God. Hence, it is not merely that they justify another person's sin, but that they are under the wrath of God themselves, having never moved from death to life, and view what is sexually immoral accordingly (Rom 1:32).
Those who call themselves Christians, but are not moving away from sexual immorality, therefore, need to be placed under church discipline, as per 1 Corinthians 5-6. If they do not repent after being rebuked by individuals and the church, as the Lord Jesus commanded in Matthew 18, they are not to be considered true believers, and we are not to associate with them.
Those who are Christians are moving, even if imperfectly so, toward sanctification, i.e., the abstaining from sexual immorality, because it evidences our move from being under God rejection of us as His images, i.e., as agents of death, into our acceptance by God through Christ as agents of life.
Anyone who does not take all of the biblical evidence into consideration as the context for all other statements is merely playing games with the text and attempting to, once again, distort the nature of God in order to distort the judgment of God upon sin. Ironically, he or she is playing out the very scene described in the text.
But let's be real clear. Homosexuality, and like sins of sexual immorality, are not mere sins practiced by people who are all equally acceptable to God in Christ. It is the revelation that God's judgment is upon us for our having distorted who He is. As such, comforting people who remain in it, rather than calling them away from God's judgment through the gospel that would cleanse and move them toward sanctification, can be described as nothing short of evil.