Still, I'd observe this is tied to basic human nature & sexuality. Unlike slavery, as best I can tell it cannot be done away with, short of making it illegal for a man to have a hot woman/entourage of women present (totally not a sexist law, btw)
I bring up the parallel, again, not because it's an equivalent situation, but to illustrate what I think is a common ethical trap we can fall into: what good is it to see an injustice and wave our hands, saying that it's just the way the things are?
You suggested that the grandposter is blindly optimistic for wanting to change the way men relate to women in the workplace (or something like that), but think about how much has changed culturally, that we can have this conversation in 2010 and have it be basically a given that human bondage is morally wrong? It took a law in 1865, and it was controversial at the time. Today you have to be on the fringe of society in order to believe that it was ever morally defensible, presumably. That's not a triumph of law, it's a triumph of active social change.
I believe this issue is fundamentally rooted in sexuality, and I am deeply, deeply fearful of the day we attempt to legislate the nature of sexuality.
As for the question of our fundamental nature, we'll just have to leave it up to the philosophers. I appreciate your good natured debate, nonetheless.
To take a more modern example, the same is true about compulsory military service. Many people once believed and many still believe that conscription is simply way cheaper than voluntary military service. However, the people that are drafted into the military service could instead have been involved in the productive work in the regular economy, and paying taxes that may be used to pay volunteers.
In short, "pure economics" doesn't automatically go in favour of slavery.
Slavery was a sustainable institution not just because it was perceived as cost-efficient. It required general acceptance of the idea that it's OK to deny certain classes of people -- e.g., according to their origin -- their basic rights. And that is pretty much about racism.
You: "Slavery is a terrible thing."
Yes, I agree with your statement, but it went way beyond anything we're actually talking with in order to elicit agreement from readers. You characterized the previous comment as being pro-slavery, hence creating a strawman argument.