The thing is there are people who are more or less likely to be worth listening to. Even if no one is actually evil, some people don't have ideas that are generally worth listening to. They might occasionally have a good idea. And even people with generally good ideas might have a few really bad ones. The question that needs to be asked is not "is this person good or evil" or even "is this person smart or dumb" but rather "what is the probability that I will learn something interesting and correct from listening to this person?"