Two things firstly:
1. I deeply respect the Judeo-Christian tradition, particularly in its Catholic expression. I spent six and a half years in a Catholic seminary including four years in Rome, so I know something about it.
2. I am in favor of gay marriage.
Although the Catholic church will never grant gay marriage equality, it should grant it recognition.
Gay marriage is an issue for the secular state. The church doesn't own the term 'marriage', much less the legal architecture surrounding it.
The official Catholic position is that the sacrament of marriage, in its 'fullness', can by definition only be between a man and a woman, as only such a union is fundamentally 'open' to the pro-creation and nurturing of children. (Concepts such as fullness and openness have a long history in Catholic thought.)
But Catholics can believe in the primacy of heterosexual marriage without resorting to a mindless denigration of gay marriage. In fact surveys show that a majority of Catholics are of that persuasion.
Catholic thinking on homosexuality, like contraception, is still very immature. Orthodox moral theology demonises the 'sin' as ontologically evil, but forgives the 'sinner'. This means the church has a long way to go before it will even come close to embracing gay unions, much less celebrating them liturgically.
There is no conceptual conflict on other issues of faith and morals like divorce and abortion which the state allows in specific circumstances and Catholic belief doesn't.
Christendom is long gone. We live in a secular, pluralistic, tolerant, multi-faith society, ironically a gift of the Judeo-Christian tradition. It is no longer realistic for Christians to expect, much less demand, that society honour without qualification their particular belief and value system.
Believing in religious freedom also means believing in the legislative freedom of the secular state. The church can organise, protest, lobby and persuade, but it cannot de-legitimise.
Perhaps one day, after an adult church abolishes celibacy and ordains women and the openly gay, it will find itself ready to celebrate and embrace gay unions, thus honouring the deep love and public commitment of the participants.
I'm not one of those who believe this will never happen. The Holy Spirit resides in the people, and the people will eventually have their way.