Mixed race marriages were not (and are not) the norm for any society.<quoted text>
Let's take your fourth point and apply it for today. Same sex marriages are unnatural. They have never happened as a norm for any society. Homosexual sex is unnatural because the body was not made to complement same sex. Its unnatural in the way that it destroys the body via diseases that result from it.
The sexual activities of homosexuals are also done by heterosexuals, so are you against allowing heterosexual couples to marry if they practice cunnilingus, fellatio, and/or anal sex? Would you allow same-sex couples to marry if they are celibate? We allow inter-racial marriage despite its place as a deviation from the norm. Nothing you said same-sex couples do is off-limits to heterosexual couples, and you surely don't see "not the norm" as a reason to prohibit particular marriages. It sounds like you're simply against marriage.