Sounds nasty, doesn't it? That's because it was meant to. Miscegenation is what people used to call interracial marriage back in the days before it was lawful in the USA . The theory behind prohibiting it went something like this:
God created separate races for a purpose. Mixing the races defeats that purpose. Therefore, people of different races (black, white, asian,, hispanic ) should only be allowed to marry people of their own race.
This logic went essentially unchallenged until 1958, when Mildred (who was black) and Richard (who was white) Loving got married because she was pregnant [3, 4]. Because Virginia would nor grant them a license to marry, they went across the state line to Maryland, where they could and did get hitched. When they came back to Virginia, the state prosecuted them for “cohabiting as man and wife, against the peace and dignity of the Commonwealth” ; in return for a guilty plea and an agreement to leave the state for 25 years, they were released. They moved to Washington and then began working to have the law overturned. When they wrote the US Attorney General, he referred them to the ACLU. In 1967, the US Supreme Court heard the case and overturned their conviction based on the “full faith and credit” and “equal protection” clauses in the Constitution.
A similar battle is raging now, over whether or not two people of the same sex have the right to get legally married  and to have the decisions about marriage made in one state be valid in another . Constitutionally, this is a mixed bag. The equal protection clause probably doesn't apply, as this legal distinction is based on the sex of the two people (which is not explicitly recognized in the clause), rather than their race (which is). However, most readings of the full faith and credit clause would argue that the legal contract  known colloquially as “marriage” issued by one state should apply in others. If the ultimate decision is “no”, then this opens the doors for every state to impose its own laws regarding credit , banking, and other interstate transactions – which was the mess that forced the Confederacy to call it quits and re-organize as a republic .
Several solutions have been proposed for this conundrum, from the adoption of a constitutional amendment to define marriage to separating the legal and religious definitions. Fallacious arguments abound on both sides, from the “marriage has always been between one man and one woman”  to “the Christian church has always recognized gay marriage” . About all that can be said for sure is that, given that this is an election year, we can expect to hear a lot of noise and see a lot of heat generated over this issue – but have very little light shed on it. And no matter what the solution that they come up with is, there will be a lot of people who hate it – and it will cause more problems than it solves.
(This post inspired by an article on the aptly-named Mildred Loving, who challenged miscegenation laws and won.)
 Not to say it didn’t happen; it just wasn’t legally recognized by many states.
 Senso stricto, “asian”and “hispanic” are ethnicities, not races. And biologically speaking, “race” is a null concept. There are subspecies of animals, but humans are less varied than many other species, perhaps because of that close call we had some 70,000 years ago.
 Not to say that folks didn’t micegenate; they simply didn’t make it legal. After all, if they hadn’t been mixing, then we’d never have such evocative terms as octoroon, would we?
 In the 1950’s, being pregnant and unmarried was considered a bad thing and often was said to be “the girl’s fault” [a]. In the 1850’s it was not unusual – and frequently was considered to be part of the courting process [b].
 This law is still on the books in Virginia, BTW! However, the ACLU has challenged a similar law in North Carolina, which means that this law’s days may be numbered.
 As opposed to the right to get married in their church. The latter is not in doubt, except when more than two people want to get in on the fun.
 As previously noted, we’ve been down this road before. First with racially-mixed marriages, and then with “no fault” divorces.
 Socially speaking, it is a contract under state laws.
 Instead of everyone coming under Delaware’s business-friendly laws that permit universal default and other annoyances.
 What? You didn't know that the US was a confederacy before it was a republic? Where have you been?!?
 Er, no; it hasn't. Even if we just go by what is written in the Bible, there are numerous counter-examples from Lamech's matched pair to King Solomon's 700 wives. If we use what is observed in the world around us, there are customs ranging from the Romanesque primogeniture-based monogamy to the more common polygyny to the rare but interesting polyandry. About the only thing that humans don't seem to want to try is abstinence…
 Er, no; it hasn't. Though the original church was more likely to engage in free-love than in monogamy [c], very few sects of the Christians have ever accepted homosexuality (though many were willing to wink and nod at it).
[a] Though the last time I checked, there was only one birth on record where a man wasn’t involved.
[b] Hence the adage about eager brides being able to do in six months what took cows and countesses nine.
[c] Where do you think that bit about the “holy kiss” came from?