In many cases it's not exactly 'known evidence'. If your social environment keeps indoctrinating you to not trust the actual evidence and see it as evidence, then to you this is not 'actual evidence'. In reality it is off course, but you are blinded by your environment to see it as such. You are still mistaken, but not because you have a mental illness that makes you over-fantasize and lose contact with reality. It's because one is a social creature that relies on it's social environment to construct it's worldview, in which these flawed and mistaken convictions are amplified rather than discouraged.
I understand what you are saying, and I agree more or less, but this is going to be about semantics, which I ordinarily hate, but since it suits my needs at the moment, I'll get into semantics: LOL
As Solitary pointed out, we are all a little bit crazy, and I mean this to be taken literally. We are indeed all a little bit crazy, and if we take an honest look at ourselves, we can find traces of various mental illness listed in Abnormal Psychology texts to varying degrees. And I'm pretty sure to be legally declared "insane", all that is required is the opinion of a psychologist that one of our "traces" of mental dysfunction crosses an arbitrary line by some arbitrary degree or two, where the psychologist determines the dysfunction to be great enough to be worthy of a diagnosis that he writes down on an official form.
I'm not really disagreeing with you, because each of our environments includes the peer pressure you refer to, and I fully understand the power of that. We are all effected by such pressure, some more than others. It's a sliding scale as to how much we are affected, with someone who is totally controlled by those pressures and who is totally incapable of deciding anything on his own, crosses an arbitrary line and could be diagnosed by a psychologist as being "crazy." Dependence on the thoughts of others comes in degrees, we all do it. Doing it to the point of a diagnosis of "crazy" is just where the dysfunction crosses an arbitrary line.
When I look back on my past, I see this dependence in myself. Just because my parents and other authorities declared utter bullshit to be reality, I believed it. and I call that crazy. Many psychologists don't and Christians never would, but it is what it is, and I call it crazy, just not to the extent where institutionalization, or drug therapy is demanded by society.
Well, that's my opinion. I don't expect others to agree, but I did have fun trying to explain what I meant. LOL