If God had intended love and marriage for opposite-sex couple only, then He would have never allowed homosexuality to exist in the first place. Love is love, and no matter what, you can never steal that right from someone, no matter what their sexual orientation is. Gays, lesbians, bisexuals, and transgenders have no control over their sexual preferences and should not have to deal with so many ridiculous life obstacles just because of how they were born.
If you oppose same-sex marriage, it doesn't matter if you otherwise "support" gay rights. By denying two people a proper ceremony to define their bondage, you're still imposing your own exclusionary stance on a religiously moot subject. Besides, in the practical world, why the hell does it even matter if two people of the same sex want to get married? If you base your argument on the Bible, then you may as well condone slavery, prohibit the eating of shrimp, or do anything else that contradicts the loving, open-minded attitudes expressed in later books. You can try and live by every little detail written into the Holy Book at once, and it won't work in real life. If the preservation of marriage between a man and woman is what you choose to emphasize, then unless you haven't thoughtfully considered the issue, your only justification for preventing same-sex marriage is at least some subtle form of bigotry.
How about the issue of raising families? So what if two people of the same sex can't technically have a baby together? That doesn't mean they shouldn't be allowed to love each other, marry, or even raise a family. My aunt happens to be married to another woman, and they've raised two highly thoughtful children of utmost integrity. I just saw them for Thanksgiving break, and I had such an amazing time with them. The ability to raise a family has nothing to do with some non-pliable model of two opposite-sex partners. It has to do with the parents' personal care, skills, and willingness to educate and breed their children into responsible human beings.
LGBT people have no right to be treated as second-class citizens in any way, shape, or form. We simply can't tolerate a society that intrinsically favors heterosexuals over other sexual minorities. I've seen and heard of far too many stories about of the bullying and suicides that occur to them as a result. So many of the my closest friends happen to be LGBT, and they're some of the most compassionate and human people I've ever met. They deserve far better than what our country gives them.