I think that thoughts can be plenty harmful. The only reason we don't punish people for their thoughts is that we have no way of reading people's thoughts. Realistically, if everyone's thoughts were on full display, a lot of people would be getting castigated, watched, and/or detained.
Does a consensus define evil? Is evil only something that is culturally relative? A city of drow would reach a very different consensus about what is evil than a village of halflings, would they not? I feel like D&D, at least, has a sort of idea of cosmological evil, which goes beyond what any particular people think of as evil, or even beyond a creature's actual observed behavior. A demon could be on his best behavior and not actually running amok murdering people, but still be fundamentally evil.
