Know that professors are challenged a lot. They are trained to push limits, to always defend themselves or rework their position when they are defeated. It is an intellectually tough world and it shapes the person. But it may be different in different fields.
They may look at you like Aragon does, at 2:00 here (The Prancing Pony scene)
https://www.youtube.com/watch?v=bYFPxU9xGZI
Not to discredit your intuition, just my experience of meeting professors.
About people in general: I think there is tranquil dark, and evil dark. The first one is mastered and requires skill and maturity and ability to be more selfless (or the darkness will consume you). The second is based on simple-minded selfishness, greed etc, and the darkness consumes the person.
Some people have to live in darkness, but it does not determine the core character. But stay away if unsure.