I never said it was necessary, only that it was universal. I suspect that the recent aversion to slavery is more of a function of our relative level of develop

I never said it was necessary, only that it was universal. I suspect that the recent aversion to slavery is more of a function of our relative level of development (and the education that comes with it) than anything else. Morality can only thrive when there is a reasonable standard of living, otherwise people will find ways to justify evil. Today it seems that we are at a level of development where we can only justify slavery if it is out of sight. I hope we can advance further, but we may be at our limit, as other moral taboos are already breaking down.