I respect your point, but, I have always viewed morality as changing and ethics as immutable. I do believe that it is acceptable to judge people based upon the morals of their times and since as you so aptly point out, many people living during the time of slavery opposed it and many who engaged in it, like Jefferson, knew that it was immoral and practiced it anyway, the point is that the morality of their time does not excuse them and their hypocricy exposes them.