Same reason there are murderers and others who commit the most...

Same reason there are murderers and others who commit the most heinous of crimes against the innocent.

If you are an atheist:

- You should be able to rationalise that he was of course one of the most evil characters to grace this earth and what he did serves as a reminder of what is possible if some have their way - the good versus bad argument.

If you are a believer in god:

- Hitler's soul is tormented eternally.
- Those who he killed are in a good place
- Hitler did not achieve his goal - he lost

In fact, if you believe in god, the first rationale also applies.

Those here who idolise hitler and his aims are clearly in one hell of a screwed up mess.