"If we change traditional marriage, it's a slippery slope," said the man at the table next to me at the Cheesecake Factory. "Soon we'll have people marrying animals." Ah, the straw-man or what I dub the straw-horse argument. That is, if we change traditional marriage between one man and one woman, suddenly it's the end of civilization as we know it and bestiality rules.
First, there's no such thing as traditional marriage. Traditions change over time to meet social, economic, religious, and cultural needs. In the early days of the Christian Church, marriage was not a sacrament, as was baptism or the Eucharist. It took more than a millennium -- until the twelfth century -- and lengthy tracts from theologians and popes to make it a sacrament. The early patristic writers assumed, as did Roman law, that consent defined a marriage. In fact, there were arguments about consummation even being a criterion for marriage. That is, a couple didn't have to go to bed together; what counted was that they consented to be married. The Decretum of Gratian, a twelfth-century jurist, tried to harmonize the different laws regarding marriage. Gratian believed that consummation transformed the union into a "sacrament." There was no single wedding ritual in the Middle Ages, and the Catholic wedding one might see today dates from the sixteenth century. Reformers like Luther and Calvin were pro sex within marriage, but they opposed marriage as a sacrament.
What about other traditions? For Germanic societies in the early part of the first millennium, which had influence over England (think Angles and Saxons), the dominant social element was the larger kin group. Kings and their followers married early and often. Richer men favored polygamy and kept concubines. Marrying one's cousins was encouraged to keep wealth within the family. Legitimate marriage was contracted by capture (Raubehe), by purchase (Kaufehe), and by mutual consent (Friedelehe). Purchase was the preferred method. Lack of consent from kin forfeited betrothal and dowry agreements, and the husband did not acquire legal power (Munt) over his wife. It's unlikely my man at the Cheesecake Factory meant these traditions, which eventually merged with those of the Christian Church.
Second, I'm not aware of any man-horse association that's lobbying Congress or state governments to allow bestiality. Most societies historically have imposed criminal sanctions on sex between people and animals. Also, it's a more of an issue in rural societies among people who live and work in close proximity to livestock. The trends over the last century show us moving to urban and suburban areas, with the number of farmers reduced. So far as men and their horses in politics go, Caligula allegedly tried to make his horse, Incitatus, a Roman senator, a consul, and a priest. Of course, the truth of these accounts is debatable, as the documenters could have been pointing out his insanity or poor government. My favorite is Gerald of Wales's account of the sexual perversity of the Irish kings in his twelfth-century The History and Topography of Ireland. Among a host of unnatural and strange things, including prophetic werewolves, fish with golden teeth, a man with limbs like an ox, and a lady with a beard in love with a goat, Gerald claims that the Irish kings practiced a ritualized form of bestiality. The king-to-be would mate with a white mare, slaughter the animal, boil the pieces in a cauldron, and share the meat with his subjects. Gerald, ostensibly, wrote this for King Henry II to justify the throne's imperial claims in marching into such a barbarous nation to civilize them. However, Gerald had his own agenda, as he hated Henry II and felt his own Welsh relatives had a better claim to march into Ireland.
So what would Mr. Ed say to all of these political fictions? Probably, "Oh, Wilbur."