mathanxiety, Yes, that sums up my understanding.
So I ask again to anybody who is still reading this: Given this, how can a catholic believe that gay marriage to be acceptable? Their church has said it is wrong!
It is surely a fundamental part of the RC faith to believe in the grace of god being passed through the holy union of marriage between man and woman to produce children?
KEY POINT: This belief is not in isolation: it is tied up with no sex before marriage, masturbation being wrong, contraception being wrong as sex is for reproduction.
Honest to goodness: how on earth anybody can call themselves a Catholic and be pro gay marriage, pro contraception, pro sex before marriage - it is just fecking ridiculous.
I know that the church is sympathetic to homosexuality and doesn't-as I had previously though- condemn them to hell. I was wrong about that, I admit.
But it's definitely NOT acceptable for them to act out of their desires because sex outside of marriage is wrong and they can never marry because marriage is between a man and a woman to reproduce. So, logically, celibacy is the only choice! How can gay people reproduce naturally, anyway?! 
Even though I am an atheist, I have to say all of this makes complete sense in the context of catholicism!
And, sorry, belief in a loving god is all very well and good but, really, Catholicism is about MORE than that.