Poppycock. At that time most nations on earth practiced some sort of slavery. In a had slaves in N. America before Columbus landed. It is neither an American sin nor a curse. It was and in some places still is man's inhumanity to man.
We've dealt with the aftermath badly, and Obama has set our progress back decades.
I’m not talking about other countries. I’m saying that regarding the US, even if “everybody else was doing it”, it is one of the defective genes that was destined to get us.