The church hasn't always preached things that are 100% based on the Bible. The Bible is my main guide, and I don't see it shunning interracial marriage. It does, however, shun Gay relationship and marriage.
Church doctorine based off of this is clear, and if a Church wants to ban gay marriage, why not?
A government still can give the right to a civil union. It's a simple matter! Churches=Marriage, Government=Civil Union. Civil Union rights=Marriage rights (or should in my opinion).
As always- None of my statements are evaluated by the FDA.
My advice is not intended to diagnose, treat, cure or prevent any diseases unless prescribed by a health practitioner. All information is provided for educational purposes only and should not replace the advice of your medical doctor.
(but your medical doctor will probably end up killing you