[Natsu]

I believe the idea is that human notions of 'evil' are based on imperfect knowledge, at best. Therefore, quite often one person's 'evil' is another's 'justice' and letting people rampage in pursuit of it does not make for a peaceful society. Rather, people have to be able to work together in spite of their differing ideals, instead of hoping to be able to eliminate or marginalize everyone who might not believe the same thing.

[pekk]

On the other hand, if what other people believe is outlined in Mein Kampf, the attitude that you should work together with those people in spite of your differing ideals is quite wrong. We know this because of what happened in the Holocaust. Today, we have the luxury to judge this tree by its fruits. Even if someone else believes that the Holocaust was justice, there has to be some line of appeasement we won't cross, where we say "no, this really is evil" or we become complicit in worse things than just war, and will only be able to recognize that in retrospect.

This becomes concrete when we are talking about a state which formally supported the Nazis.

[Natsu]

The Nazis would be a good example of a group that rampaged in pursuit of their ideal of "justice"--they believed that a group of rich people (Jews) were the source of all misery, however removed from reality that might be--then rampaged, not just in a figurative sense, but also a very literal one (e.g. kristallnacht).

I quite explicitly said that this was both an undesirable thing and something to put a stop to.

[Aeolun]

This is only true if you are the only one to follow that rule. Someone whose belief is outlined in Mein Kampf, but nonetheless follows the same rule, will seek other means than the historical of resolving his differences.

[Natsu]

No, it's more a matter of the problem not being their ideals, but what they're willing to do in pursuit of those ideals. I mean, you can find plenty of commonality between Nazi ideals and plenty of other beliefs, but most of them aren't trying to carry out mass murder. And of the few groups that are trying to commit mass murder, like Isis, I think we all agree that they're terrible.