It doesn't matter what we know today because slavery has always been wrong. By keeping slaves Jefferson was behaving immorally. He might have believed that he had a right to take away a mans freedom but how could he have ever actually had the right? The majority of people didn't think he was a monster but some forward and right thinking people did because there is no justification for keeping slaves just like there were forward thinking people in the deep south in the past who knew it was morally wrong to lynch a black man (or any man for that matter).

If there were 50 white men at a Klu Klux Clan meeting and a black man walked in, the majority of people at the meeting would agree that the black man had no rights and that they had the right to harm the black man but the black man would disagree. Who would actually be correct? Did the Klu Klux Clan actually have the right to harm the black man because the majority believed it and because there were racist laws in existence that allowed them to justify their actions in their heads?