People who supported interracial marriage laws thought they were right...they were certain their churches wouldn't ever marry "those people".
Remember that people who thought themselves to be Christians slayed thousands of people trying to make those people turn to Christianity. Were those people true Christians? Hell no.
A person has no choice to be born American, or white, or black, or Hispanic, or anything else. No one would choose to have a child born with a disability.
Homosexuality IS a choice. Just as adultery, and promiscuity, and even a consenting man and woman living together sleeping in the same bed. Those are all choices that people make.
Interracial marriage is not a sin, a Christian marrying an unbeliever, that is considered a sin, according to what I know of the Bible. Others believe differently than I do, but we still search the Scriptures for the answers to all kinds of questions, the key is to keep on searching, for Christianity is a learning religion, and as we grow, we learn and we adapt. The basis for our faith is the one true constant. John 3:16, if you have that, and you truly believe that, you will want to learn more.