Peter Brown
Sex was shocking to the early Christians. Sex in the Roman world was intimately linked to slavery. Ergo: Christians, once they came to power after the year 312, predictably hammered the sexual codes of a society glutted on the ready availability of servile bodies and even cut away (if somewhat more tentatively than we might wish) at those parts of the slave system—such as prostitution—that fostered sexual indulgence.
http://www.nybooks.com/articles/archives/2013/dec/19/rome-sex-freedom/