I wonder if a useful analogy to those of us who, as Christians, are bound to love the marginalized that cultural liberalism seeks to help, but cannot get on board with cultural program of left liberalism would be the situation of those who sympathized with the plight of the poor in the late nineteenth century but refused to become socials or communists (esp. the Church). I suspect they were similarly denounced as heartless (and, in fact, in some places, it's still the case that anyone who doesn't get on board with radicalism is denounced as being anti-poor.)
The analogy may fail (in the case of the Church, at least) because the nineteenth century poor were seen as victims of capitalism, and the Church vigorously denounced the capitalism behind that development as much, if not more, than socialism.
But maybe the analogy does work--or it would if we could more clearly frame the isolation of the marginalized as a symptom of the broader breakdown of society--families (nuclear and extended), communities, etc.--and, within the Church, the celibate vocation. In other words, gay marriage is a radical solution like socialism that we must reject, but it arises because our society is atomized and has subverted the meaning of family and sexuality. The solution isn't more individualism and false liberation, but a return to a thicker, religious, society that doesn't make sexual fulfillment the highest good and companionate marriage the only permanent relationship.
Of course, it was easier to triangulate against capitalism and socialism because the Church was seen more a regressive obstacle--the opiate of the masses--rather than the source of oppression itself. In the case of gays at least, the Church is seen as the prime oppressor, and the left doesn't really identify social atomization as the enemy. (Or it equates society with the state, so when it opposes individualism, what it advocates is a larger, more invasive state rather than a thick society where people are directly responsible for their neighbors.)
So, not a perfect analogy. In the end, the Church's rejection of radicalism was vindicated when communism invariably led to oppression, starvation and mass murder. Communism openly advocated violent revolution from the beginning, so it's an exaggeration to compare the cultural left to it in that regard--whatever totalitarian tendencies it may have, it's not advocating violence. (Of course, being in control of the state, which has further consolidated its monopoly on violence in the last century, they don't really have to.)
