The concept that demographic factors don't confer favored status upon somebody is a pretty basic Christian teaching, but many Christians are still gonna be loathe to condone same-sex marriages. Equality between men & women is tricky: men & women can be seen as equal in Christ, but they can also just as easily be seen as having different roles to play in the life of the church.
Men and women were ordained to complete each other by joining as one flesh and forming a household together. C.S. Lewis compares this to a lock and a key. The sexes are different, and this difference reflects God's intended purpose for human sexuality, which as all parts of human life is inextricably linked to the Church. There is simply no comparison to skin color here.
I will say the lock and key analogy is probably one of the worst ones out there, and to be honest when I see it I almost always see it in a way that tries to shame women that have many partners while justifying men that do; almost to the point where it has become a meme of sorts ("A key that opens every door is a master key; a lock opened by any key is garbage")
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