Slavery is the biggest stain on the history of humankind. It is really hard to believe that humans would treat other humans like animals. Similarly, Holocaust should have never happened, it is if not the most then one of the evilest things humans have ever done to other humans. At that time, these were totally legal practices and it took humans hundreds of years to realize how horrible these practices were. What do you think are the horrible things we are doing right now that would shock our future generations?