The Nazis are considered the worst people on Earth, worse than Mao and Stalin, who both have higher kill counts, not because they "killed a lot of people", which is just bullshit. They're considered the worst people on Earth because they deliberately and systematically killed millions of people in specific social and ethnic groups. And here's where the comparison falls completely flat. Yes, Mao is responsible for the deaths of 78 million people, but he didn't set out and go "I'm going to kill these 78 million people because they're Jewish/homosexual/Japanese". In fact, if I remember correctly, and I cannot look it up at this exact moment, most of those 78 million deaths was due to famine. And that's the difference. Mao's policies killed people, but Hitler set out to kill, hell, set out to eradicate specific groups of people. And that's the difference, and that's where the comparison falls flat on the ground.