At First Things, Ron Belgau is only beginning his "meditations on how Christians should understand and respond to contemporary debates about human sexuality," but I already don't like where he's going.
1. To "cast stones" in the context of John 8 is to execute a sentence after a judgment according to the law. It is the carrying out of the sentence. Christ's response is a world-historical event of mercy, but it is not the suspension of the judgment that the woman has sinned (and Belgau makes this latter point, though weakly, in #8). The woman was "caught in the act of adultery" and there is no doubt--in her mind or in anyone else's--that what she had done is sinful. The normative meaning of "neither do I condemn you" is mercy, a condition of which is the knowledge on the part of the sinner that he has sinned, rather than the absolute tolerance of sin. Mercy is loving and knowing, not loving and ignorant--for both the I and the Thou. Mercy "builds up," and part of its grace is that it allows the one who has been spared to "go forth and sin no more."
2. So knowledge has everything to do with the normative aspect of Christ's response in this passage: self-knowledge, yes (and who would dispute Belgau on that?), but also the knowledge of others, and especially the public and private knowledge of what is sinful. It is by no means clear that contemporary "sexual ethics"--in the midst of which the Christian must appear--has universal force or that it comprehends sin. There is no longer any Law or covenant to provide the context for a debate about punishment. Most Christians, when they argue against homosexual behavior, imagine themselves to be in the "knowledge" phase of mercy: the always-already loved sinner needs to know that they have sinned.
3. The public working out of "sexual ethics" is obviously cultural and political. Christian attempts to instill a public sense of sin is fraught with controversy, but also with the whimsy of public consciousness. If same-sex "marriage" is "in the zeitgeist" (and, more importantly, entering into the constitution of this country), it is not at all remarkable that opponents of SSM would overlook Newt Gingrich's adultery/remarriages and prefer him to Romeny. An adulterer or serial monogamist can make conservative policy just as well as someone who believes they will be with their wife and children even after death.
4. Talking about "power" and stigmas within stigmas is almost totally unhelpful. You don't need to feel sorry for the Samaritan woman at the well to get the message about "true worship." You need to know that she's different from the Jews and that she takes some solace in the fact that her race has remained where Jacob used to be. It's a different, related story.
5. You can't mix divorce and same-sex "marriage" or homosexual behavior in general if you're not going to make clear whether you're talking to Catholics or to Christians in general. Not all Christians "condemn" divorce. I suppose not all Christians condemn homosexual acts either, but that a less significant "all." There's a reason only gods and kings are properly merciful. They have authority. Christians hardly have authority in their own churches these days.