Assemblywoman Bass's comment about the "Tide of History" to me raises the really interesting question about ancient sexual practices. Despite the individual variations in Greek practices, I think it is fair to say that if you look at the Greco-Roman world as a whole, you will find a general acceptance of many if not all of the sexual and sexually-related behaviors that are so controversial in our time---abortion, same-sex sexual activity, prostitution, non-marital opposite-sex sexual activity, youth sexuality, etc. In other words, much of the progressive project in regards to sexuality is in many aways about returning to the Greco-Roman model.

And yet, the "Tide of History" to a sharp turn, and in a relatively short period of time (maybe 100 to 150 years) the ancient cultural consensus was comprehensively rejected in favor of the more restrictive Christian ethic. And this was done mostly in a bottom-up fashion--I've read some scholarship that argues that Constantine's embrace of Christianity was more about recognizing the reality that his empire was mostly Christian already.

If the progressive/ancient sexual ethic is "better", why were people so eager to cast it aside? Clearly, a bunch of people wanted to give up the fun times, or at the very least thought that the benefits of the new order outweighed the sacrifices.

That change, to me, is where we should be looking for lessons.

One interesting clue is that many of the early Christians were women, disproportionately so. Perhaps Christianity, in its earliest form, offered advantages to women compared to the alternative systems at the time (it's all relative). For example, monogamous marriage, fidelity required for men as well as women (at least theoretically), not being forced to kill a newborn that was sickly or female just because the pater familias said so.

Monogamy also benefits poor men, when compared to polygamy. If a few rich men are hogging all the women, that's great for them but not so much so for the less well-off guys. The "blessed are the meek" stuff probably also appealed.

Of course, once Christianity became part of the state, it was completely different.

Don't forget disease. As time went on and human knowledge expanded it would seem Christian sexual values were more in line with limiting disease prevention, inheritance, and cost (supporting one wife is easier than supporting five).

There's more to this than what you've already named. The "Christian revolution" in Roman times, if you will allow me to call it that, was a revolution of middle-class people against the disturbing upper-upper-class "morality" of the times.

That is, sexually exclusive, one man/one woman, child-producing marriages were already the societal norm among the vast majority of the population, and the growing middle class was disgusted by the decadence and licentiousness of the tiny ruling class. The result was what we now think of as "Christian sexual morality" (you could as accurately call it "3rd century Roman middle class sexual morality") being seen as reasonable, prudent, and less likely to result in someone trying to poison you over breakfast.

The Victorian era was a repeat of this discovery: Its "prudery" (funny how those supposedly anti-sex people managed to produce so many children) was a backlash against the sexual freedom of the Regency era. During the late 18th and early 19th century, adultery was commonplace in the upper echelons of British society. See Lord Chesterson's letters to his son, which advocated "the morals of an alley cat", to quote a modern reviewer. Truly scandalous behavior required something more. In the Regency era, one high-born woman decided to make herself the talk of the town by appearing at a major ball in a thin gown that she had soaked with water in the "Cyprian style", which leaves less to the imagination than a wet T-shirt contest.

These sorts of public-knowledge sexual displays were disgusting to the middle and working classes, who were constantly being told that these people were their "betters". The effect on individual humans was apparent to them, from the trauma that the illegitimate children suffered, to the distress of the families, to the horrible effects on less powerful people, such as the servants in the household. (Would you send your daughter to work in any house with any man brought up to think that bedding anything wearing a skirt was his right?)

It's no wonder that rational people looked around and decided that the instability and distress that unbridled sexual license created was not good for society. I have some hope that we'll re-discover the same thing in another generation.

If the progressive/ancient sexual ethic is "better", why were people so eager to cast it aside? Clearly, a bunch of people wanted to give up the fun times, or at the very least thought that the benefits of the new order outweighed the sacrifices.

I'm not convinced anything was cast aside. It's worth noting that homosexuality--whether we're measuring homosexual activity as a percentage of total sexual activity or the absence of heterosexual attraction--seems to occur at comparable rates in highly restrictive societies and highly liberalized ones. If there's not much difference between how often it takes place in Iran (where it can get you caned) and how often it takes place in the Netherlands, I have some doubt as to whether the actual occurrence of homosexual activity or homosexuality as a state or condition really decreased post-Constantine. It's just a matter of how discreet you were in pursuing it.

As to why the rest of society was so quick to change views . . . well, if you believe in deity--not just a metaphysical principle (I certainly believe in that), but in a "personal" (essentially anthropomorphic) god fraught with moral preoccupations and behavioral dictates (I don't believe in one of those, but some plurality, if not an outright majority, of people does)--that deity's admonishments might seem a good reason to behave according to its dictates.

Then again, I'm not sure we even need to go there. Most people are heterosexual, heterosexual unions frequently produce offspring, and around offspring we see family units arise. Even prior to Christianity, there were family oriented social structures, religious or otherwise, and even among Rome's urban elites, my guess is that the debaucheries of some were as anomalous as they had been before, or would become later (if considerably higher in profile).