The truth behind the gates of Auschwitz: A shitload of people died for no reason other than the hatred of others who happened to have a shitload of power and that's just fucking awful, as far as genocide goes it's probably the one with the second or third most deaths, the one with the most probably being that of the Native Americans (an estimated 80-90% of that whole population, but more died from smallpox than human action)
Some people don't know that the Nazis put more than just Jews to death because of their views. Homosexuals, disabled people, Communists, ethnic minorities and gypsies to name a few. I wouldn't be surprised if more than 6 million people died.
The Holocaust is something that as a species we must never allow to happen again. However, because the human race is the utter scum of the universe we'll commit another major genocide without giving it a second thought if given the chance (heck there are genocides happening right now that we're actually supporting as a species).
There's always going to be genocide in our world and there is always going to be people supporting that genocide. There isn't much we can do about that but sit back, watch and then years later try to explain to our grandchildren why we allowed it to happen.