"Isn't opposition to same-sex marriage just bigotry?"
If you are a Christian, this is something you'll be asked in the near future if you haven't been asked this directly already.
The first thing I would ask any person who asks this question is, "Do you believe in absolute morality?" Because the implication of the question is that all people should embrace same-sex marriage. That would make same-sex marriage an absolute moral good.
My hunch is that many people who see same-sex marriage as an absolute moral good don't actually believe in absolute morality, because absolute morality in any sphere of life implies God, the only one in the universe with the authority to determine absolute good. So, most people who ask this question probably won't venture down this path because the case for any absolute morality is always fraught with God.
Another implication that lies behind this question is that opposing same-sex marriage is the same as being a racist. The assumption is that people only oppose same-sex marriage because they're ignorant or close-minded or emotionally stunted, etc.
The problem with equating the Sexual Revolution with the Civil Rights Movement is that Martin Luther King Jr. used the teachings of the Bible as the basis of the Civil Rights Movement, because the Bible makes a stronger case against racism than any social-political argument ever did or could, simply because the authority of God is always higher than the authority of any government.
Some biblical bullet points against racism:
- God is not a respecter of persons (Galatians 2:6)
- God does not look at the outward appearance, but at the heart (1 Samuel 16:7)
- There is neither Jew nor Greek, but all are one in Christ (Galatians 3:28)
- Love your neighbor as yourself (Matthew 22:39)
- The Parable of the Good Samaritan (Luke 10:25-37)
And those are just a few. Needless to say, books making a biblical argument against racism and chattel slavery have been written by the scores because there is a case to be made.