I've been thinking about this one for a long time, too. Below are the most common reasons I've heard Christians use to justify their objections, and my objections to those reasons. Please read this seriously and give it some thought. If, after you have thought it through FOR YOURSELF, you still don't agree with me, that's OK. Just make sure you have reasoned and logical reasons, and you're not simply spouting rhetoric you've heard on Christian radio or whatever.
“The Bible says marriage is between one man and one woman!”
Really? Let's take a look. Yes, God created Eve for Adam. The Bible does not tell us whether Adam took another wife; however, legend does tell us that Eve may not have been his only wife.
Even if the original plan was one man/one woman, a cursory reading of the Bible tells us that this was hardly ever the case. Abraham was not criticized for taking Hagar to wife; he was criticized for his lack of faith that the promised son would come from Sarah. David was never criticized for having multiple wives, and he was called a man after God's own heart. Solomon was not criticized for his political marriages; he was criticized for permitting them to lead him away from Jehovah. The only comment on the subject in the New Testament is in 1 Timothy, where a pastor must be husband to only one wife.
Using the Bible to object to same-sex marriage mischaracterizes the Bible. The Bible does not define marriage.
“I don't want to support that lifestyle!”
Let's break this one down. You, as a believer in Jesus Christ, don't want to support a lifestyle of sin. (For purposes of this discussion, we will assume that homosexuality is a sin.) So that means that you will also not support the lifestyle of anyone who gets drunk regularly (Ephesians 5:17), anyone who uses profanity regularly (Ephesians 5:4), anyone who exasperates their children (Ephesians 6:4), etc. You get the picture. If you want to say that you cannot support a sinful lifestyle, then you have to reject all sinners, not just the ones who disgust you. And since every one of us is a sinner (Romans 3:23), are you going to reject yourself? No? Then you can't reject anyone else, either.
Let's also remember that many people who identify as homosexual are not Christians (unbelievers). Without the filling of the Holy Spirit, they have no way to do anything other than sin.
And as for the professing Christians who are also homosexual, you have not been appointed their personal Holy Spirit. Their choices are between them and God. Not your business, not mine. Your business and mine is to reflect the grace of Jesus Christ.
“Hate the sin, love the sinner!”
Newsflash: When someone tells you “I love you, but I hate what you're doing,” all you hear is “I hate.” And our God is love. Our Lord invited all to His table. He promises rest to anyone who comes. And He paid the penalty for all sin, so exactly what is it you think you're promoting? Sin has been forgiven. You don't get to judge someone else's sin, not when your Savior has paid the penalty for it.
If you're dealing with an unbeliever, the only issue is what they think of Jesus Christ. Sin is an issue for BELIEVERS, because we're the ones who have temporal consequences of sin – we're the ones for whom 1 John 1:9 is written. Believers have to confess our sins so that fellowship with God is restored. Unbelievers don't have this option. All they can do is accept Jesus Christ as their Savior.
“America was founded as a Christian nation! We have to preserve Christian values!”
Let's take a look at history, shall we? Yes, the Puritans came over to escape religious persecution by the Catholic Church and the Church of England. However, the Puritans exhibited the same astonishing lack of grace to anyone who didn't fit their narrow notion of what Christianity should be. And at that time, they considered themselves English colonists.
The move for independence from England was political, not religious. It was spurred by taxation issues and other issues regarding the governance of the colonies.
The group of men generally considered as the Founding Fathers consisted of both Christians and Deists. Some of the Christians were Unitarians rather than Trinitarians, so the idea that there was one religious faith accepted by the Founding Fathers is laughable.
If the argument is that we have a responsibility to preserve the values “on which this country was founded,” then we logically should still practice slavery, be anti-mixed marriage, and women should not have the right to vote. Those were values of society at that time. Picking and choosing societal values from history is never intellectually honest.
Besides, as pointed out above, the Bible does not define marriage as one man/one woman, so which version of those values are we espousing? Polygamy? Child marriage?
The only intellectually honest objection to gay marriage is “It's icky!” And if you're disgusted by the thought of sex between two men or two women, that's OK. You can be disgusted. But you cannot use that disgust to deny them the benefits of marriage, which is, after all, a civil institution. Marriage is defined by the culture in which you live (just think of the differences in what is required to be married under traditional Christian rules, traditional Jewish rules, traditional Hindu rules, and traditional secular rules. It's all marriage.). And one thing that is very clear is that Christians are to live in the society where they find themselves (Romans 13:1).