University of St. Thomas Law Professor Robert Delahunty has a commentary in the Minneapolis Star Tribune in which he argues against gay-marriage. Obviously, the best way to oppose gay-marriage is to patiently explain that slaveholders lost freedom because of emancipation:
Of course, some tradeoffs are desirable. No one now regrets that the constitutional amendment banning slavery necessarily ended the freedom to own slaves. But it is not an argument for that amendment that it expanded freedom without contracting it. It did both.
As Dale Carpenter at the The Volokh Conspiracy notes, "So slaveowners lost what Delahunty calls a “freedom” — “the freedom to own slaves” — when they were forced to live in a world where they could no longer own slaves."
While Delahunty indicates that tradeoff was "desirable," any such tradeoff in the area of gay marriage would be undesirable because it would make the opponents of gay marriage uncomfortable... by forcing them to live in a world where gays could marry:
True, people of the opposite sex are still free to marry one another even if people of the same sex can do so as well. But proponents of the marriage amendment argue that an important freedom is being lost: that of living in a social world in which marriage has a particular meaning and is related in specific ways to natural reproduction and family life.
In summary, the tradeoffs caused by emancipation were "desirable" because, after all, the slaves were freed, and the former slaveholders were merely "forced to live in a world where they could no longer own slaves." In contrast, the tradeoffs associated with granting gays the right and freedom to marry are undesirable because the opponents of gay marriage would be uncomfortably forced to live in a State where they saw, heard, or somehow knew that somewhere some unidentified gay people had somehow been allowed to marry. And were happy.