Jack Jack, I totally get what you're saying and I for the most part share your philosophy. Personally, I've reasoned that since good and evil, moral right and wrong, are subjective, human made concepts that they do not exist outside of the context of our society. Also, I disagree with TheAmazingFlygon who seems to think that just because the majority of people in the majority of societies have a fairly similar core of morals that this moral code somehow transcended subjectivity and becomes objective. No many how many people share and subjective belief, it is still subjective. There are still people that disagree with this commonly held morality, and because it is subjective they cannot be objectively "wrong".
Anyway, the bottom line is that I think that you cannot say that anyone is undeniable evil because there is no objective definition of evil. Therefore, Hitler is not undeniably evil. He is evil by my own personal moral code and most people's moral code, but that does not make it "undeniable".
Anyway I'd say more but I got an appointment, by for now :)