Some people think the victims invented it to get sympathy or special favors, but they are the ones who have been fooled by the real haters. The truth is that some people don't care who was hurt, or rejoice in the pain inflicted on people they hate; they want people to forget it so they can go on hating the people who were targets of the Nazis. It was not just the Jewish people they hated and persecuted. Anybody handicapped or mentally ill, anybody slightly deformed, like birth defects, anybody who looked too dark skinned or too different, like the Asians or Pacific Islanders. And anybody who did not hold to the same prejudices as them were targeted as well. So do not be afraid to dislike someone who does not believe in the Holocaust. They do not just hate people of the Jewish faith. They hate anybody not like them.
There are various reasons people do not want to believe The Holocaust happened. For many it does not suit their arguments for the Hatred they feel towards the Jews in particular, and any who do not suit their definition of a "Perfect Homogenous" Race. Other refuse to believe out of a misplaced feeling of guilt; to them it could not have happened because Humanity would not have let it, therefore it must be a lie. Some see it as merely a grand Hoax created by The Jewish people and their allies to justify the existence of Israel. While still others say it didn't without really examining their reasoning; they do so merely as followers echo-ing ignorance.