If we were in India now, there would be servants standing in the corners of this room and I wouldn't notice them. That is what my society is like, that is what the divide is like.
Marriage is an institution fits in perfect harmony with the laws of nature; whereas systems of slavery and segregation were designed to brutally oppress people and thereby violated the laws of nature.
God, our genes, our environment, or some stupid programmer keying in code at an ancient terminal - there's no way free will can ever exist if we as individuals are the result of some external cause.