Abolition is hardly condemned as many times in scripture as homosexuality. About the closest we get is a disputed passage where Paul says being a slave is irrelevant to your faith and then EITHER that you should remain a slave OR that you should seek your freedom given the chance, depending on the reading. There is nothing like the statement of how a slave can legitimately be freed to allow a heterosexual to legitimately become homosexual. There's not much endorsement OR prohibition of slavery biblically, which is why pro-slavery groups invariably fell back on "Hams Sin" and the statement he and his descendants would serve his brothers to rationalize slavery--it was the best they could do. TECHNICALLY, there actually isn't much biblical basis for prohibited slavery, as such (though there are many passages from the Torah down to the NT that mitigate slavery), it's just practically impossible to apply the Golden Rule to people considered property. However, abolition of slavery isn't something the bible, Church Fathers and Church tradition and practice for thousands of years explicitly and repeatedly condemns. If a fellow Christian told Moses, Paul, Augustine, Aquinas or Lewis he was freeing his slave he would almost certainly have been commended; if he told any of them he was marrying another man the best he could expect from any of them would be sincere regret and a promise to pray for his soul. Slavery simply never had the integral relationship with Christianity that heterosexuality does.