I don't think it's the Christ part of Christianity that gay rights advocates hate. Jesus said lots of things about love but never said one word about homosexuality while he walked the earth as God Incarnate. (Not in any version of the Bible I've ever seen.)
What they hate is people who spend millions of dollars collectively to try to write laws infringing on their freedoms, trying to force them to observe someone else's religion they don't believe in. (i.e. "Marriage is between a man and a woman because the Bible says so.")
If this still doesn't make sense, consider how you would feel if Muslims were spending millions of dollars lobbying to write a law saying Christian marriages are invalid. If you got married in a Christian church, it is not valid, not legal, you are not married in the eyes of society or the government. Why? Well because the one, true, word of God, the Qu'Ran, says so. Only marriages under Islam are valid. It's God's word. (Yes, coincidentally, those Muslims think the same thing about their one and only true holy book that Christians think about theirs. It's the only true word of God.)
So these Muslims are trying to make sure they protect Traditional Marriage, and they're going to change the law to make sure everybody is on the same page. It's for the good of society and the children.
Now how would you feel about those Muslims? Would you think they are nice people? Would you think it was great they cared so much about your soul and society that they were working very hard to take away your freedom to define for yourself what marriage is? Would you think it was great they know better than you do what you should believe and how you should form your family?
I don't agree with hate when it's just unfounded hate and prejudice. But you do have to understand, for a lot of people they have very good reason to not want to put up with Christians. Nobody is trying to tell Christians who they can and can't marry, or how they must define a word, or what they must believe. But many Christians are trying to write laws to do this to everyone else.
I'm just trying to point out the other side of this. I believe in judging every individual based on their character and actions, and I try not to make assumptions about someone just because they Christian, gay, Liberal, or whatever. Those are labels, not people.