I've actually heard less rhetoric from the Church on this subject than I was expecting to. Living in Maryland, I heard a good deal more last year and the year before that, as state recognition of gay unions was considered but stalled for lack of support, then considered again and passed.
I have expressed my own thoughts on gay marriage before; it isn't a subject I relish, not because I have any animosity towards gay couples, but because I hate the idea of meddling in other people's affairs, especially on such a scale. I have no intention of arguing further on the subject if I can possibly escape from doing so; my heart isn't in it, and there is next to nothing I can say that will not be offensive to one side or the other. Since most of my friends are either Christians or gay, or both, that's an awful lot of social circle at stake.
A lot of Catholics, especially some in prominent positions (in the Church, as lobbyists, as academics, &c.), assert that all Catholics must vocally and persistently oppose gay marriage, and that to do otherwise is to risk scandalizing our neighbors. Scandal is a technical term in Catholic theology, and means nudging someone else closer to sin; it actually comes from a Greek word that means "tripping wire." The contention is that, by remaining quiet on the subject, we encourage the passage of fundamentally unjust laws, and the corruption of our society into one even more tolerant of sexual decadence than it already is. And usually Hitler comes into it somehow, but I didn't follow that part very clearly.
Far be it from me to say that the structure of society is unimportant, or outside the Church's power to discuss right and wrong. I will say, as I have said before, that widespread support for gay marriage is not in fact the cause of marital decay in this country; that a redefinition of marriage has already happened, and gay marriage is simply the logical extension of the new definition; and that it is largely with the connivance or indifference of Christians, that that new definition of marriage came into being and overwhelmed the previous definition. From being fundamentally oriented toward the family, marriage became fundamentally oriented toward romantic love -- and that change has nothing at all to do with the supposed decadence of our age, nor with the queer movement, and everything to do with the age of our grandparents and before -- the household gods of neoconservatism. Blaming the gay movement, or gays as people, is as hypocritical as it is ridiculous.
I'd like, however, to consider this question of scandal more closely. It seems constantly to be cited in the Catholic-LGBT dialogue: not only opposition to gay unions, but to (it sometimes seems) any kind of social acknowledgment of homosexuality, from hostility to coming out to insisting on misleading half-truths as a precondition for simple hospitality.
The thing is, scandal is not just doing something that could, somehow, be interpreted as tolerance for homosexuality. (For one thing, tolerance is something we should definitely have for homosexuality, but let's not get sidetracked.) The primitive Church behaved in ways that were regarded as scandalous: their greetings of one another as spiritual siblings were so affectionate that they provoked rumors of incest; the secrecy of the liturgy, combined with references to the Blessed Sacrament, resulted in accusations of cannibalism; their insistence that Jesus and not Caesar was kurios, "Lord," brought them under suspicion of sedition. Or consider Our Lord Himself, who laid His hands on lepers, consorted with Gentiles, ate and drank with drunks and grafters, and numbered whores and political malcontents among His intimate friends. He must have really not cared about people's souls if He was so willing to scandalize people!
St. Thomas (I'm told) said that Christ never scandalized the Pharisees who protested His behavior, but that they scandalized themselves. To speak bluntly, I think the exact same thing is happening now. Scandal is a disreputable thing; and the Pharisees set great store by reputation: the very word hypocrite comes from the Greek word for an actor's mask.* But respectability can be the enemy of supernatural Love, and whenever it is, respectability can go to the devil. (It will.)
Consider what scandal essentially is. It is moving someone else away from God by your own actions, or inaction. That means that doing the wrong thing can be scandalous; it also means that doing what is technically the right thing in a way that's alienating and ugly can be scandalous. Nobody could have accused the Pharisees of breaking the Sabbath; but when they were preparing to accuse Jesus of impiety for healing (doing the work of a doctor!) on the Sabbath, He looked around at them and said to the man with the withered hand, 'Stretch out your hand.' He intended to provoke them, to break the artificial rules they had erected as an aid to virtue -- scandal is more complicated than simply allowing people to think you might be doing something that might be wrong. The worst kind of scandal is sending the wrong sort of message about who God is. And sending the right sort of message, to judge from the example of our Jesus and His chosen Apostles, is emphatically not neat and tidy and respectable -- indeed, the disreputable act of eating with Gentiles was nearly turned by St. Paul into a litmus test of orthodoxy, and he applied that test to the Pope!
It isn't only that a lot of Catholics don't appreciate the legal obstacles to the everyday lives of some gay couples -- or their not-so-everyday lives, as when bereaved partners can be shut out of the deathbeds and funerals of their loved ones, because they have no legal rights. And the point is not that the Church needs to change her teaching on the subject, it's that one element of that teaching -- that LGBT people are human, and ought to be accorded the same dignity as everyone else -- needs to be made much more explicit. The fact that a lot of people will read that and suppose my orthodoxy questionable is a perfect example of the problem: not because I'm of any importance, but because the human dignity of homosexuals should not have an aura of controversy. Justin Lee put the matter with biting clarity on his Tumblr, to which I've linked above: 'You might also have a hint of why, when American Christians are so vocally opposed to granting [gay and lesbian couples] those civil protections on the basis of our religious beliefs, it makes many gay people even less interested in hearing anything Christians have to say.'
This is not simply a question of making Catholic sexual mores palatable through gentleness of language. It is a question of setting Love before respectability, and being willing, maybe, to be accused of being a friend of sinners -- the one thing the Pharisee will never do.
A great place to start would be a serious consideration of the plight of queer persons internationally. The Church disgraced herself in the country of Georgia recently by participating in an anti-gay rally, with some of the demonstrators threatening to lash people with nettles if they showed support for the gay community there. Sixteen people were injured. Or we might look at the cruel and frightening discussions taking place in Uganda, where a bill to make homosexual acts punishable by years, even decades, of imprisonment (because putting men in prison is the best way to get them to not have gay sex) -- and even under some circumstances by death. And yet the only language we generally hear from devout Catholics in this country is that of defending the Church against the depredations of the gay lobby. The text 'Fathers, do not provoke your children to anger' springs to mind. These outrages are not a question of politics but of human dignity, and if the Church remains silent about them, rather than protesting them, then we are giving scandal: disreputable Jesus warned the virtuous Pharisees, 'The name of God is blasphemed among the Gentiles because of you.' If the Church allows herself to seem uncaring about human dignity when the humans in question are homosexual ones, she is going to ruin her credibility with a generation.
*In the ancient theater, actors wore iconic and exaggerated masks. So sort of like a reversal of a 3D film today, except that theirs really were in 3D.