I'd agree that if someone acted in real-life like Maran act in CF that it would be "evil". Mainly because there's no concept of "red aura" in real-life. Or, if you prefer, everybody has a red aura.

Also, in the real world there are civil authorities and we've delegated the task of punishing wrongdoers to them. In CF the vast majority of the world is no man's land. The existing civil authorities (i.e. Tribunal) only care about maintaining order in their protected spaces, not safeguarding peoples' basic rights outside those protected spaces.

Enter Maran. Basic assumptions:

1. There are people who are inherently bad. They will always do evil, in big ways or small.
2. We can know who those people are, because the gods give us the ability to see auras.
3. The existing civil authorities are limited in scope and are unconcerned with restraining evildoers outside their protected areas. Or, in many case, they are themselves engaged in evil acts outside those protected areas.
4. Irrespective of #3, the Maran aren't interested in simply restraining evildoers with respect to "big ticket" crimes: murder, rape, theft, etc. Even if someone with a red aura isn't engaged in those highly visible acts, we know by virtue of his red aura that he's somehow causing harm to innocents (or will if given the chance) in other small ways. Because he's explicitly <b>evil</b>. Ergo the only solution is the "nuclear option": eliminate everyone with a red aura (or get them redeemed by a deity).