Hitler's opinions, beliefs and actions are all determined by his morality, or in his case lack of morality.
The fact that he was a moral relativist is relevant since what I am talking about is morality and moral relativism.
Absolutist hold that moral rules are self evident, not invented. Morality is discovered like math is. If he was a moral absolutist he would have believed that killing innocent human beings was wrong.
No, that's incorrect.
What you and I consider to be Hitlers lack of morality... Hitler, and many people in Germany in the '30s and '40s considered to be moral and just.
And even if he was a moral relativist, it does not matter. If he believed his morality was divinely inspired, or was the "one true moral code", he was a moral absolutist. You just happen to disagree with what he considered to be universally held moral truths.
How he justifies his beliefs does not matter. Who really cares if he thought there was a universal moral code in line with his beliefs or not? His actions were equally dangerous no matter how he attributed it.
Hitler argued that the racial superiority of whites was self evident due to the stronger, more advanced and better organized civilizations that white people have built throughout history. That's how European colonialism was justified, and that's the same way Hitler justified his racial beliefs.
If he was a moral absolutist, he would believe that the universal code of morals said it was moral to kill or displace sub-human people so that racially pure people could have more living space, and thrive bettering civilization as a whole.
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What you're failing to recognize is that people don't have to agree with what you believe to be a moral truth, in order to be a moral absolutist.
They can believe whatever they want to. They can believe that mass genocide is just dandy, and as long as they believe that is in line with a universal moral code, they are a moral absolutist.
They can even make the same argument in defense that you have... They could argue that once upon a time, society thought killing people with freckles was wrong. However, since then we have learned more about universal moral truth, and found that it was never moral to allow people with freckles to live, and therefore they should all be put to death now.
You see, it can work both ways. Moral absolutism is no more or no less dangerous than moral relativism. The only difference is what you believe your morals are derived from, a higher power, or the perception of society at large. But remember, a higher power could possibly advocate murder or rape as well.... so it is not any more free from danger to society than relativism could be.