Intelligent people are introverted by nature for two reasons. First, the things going on inside their brain are usually more demanding or entertaining then average. Secondly, in their youth and teenage years, and to varying degrees later in life, they do not have people to identify strongly with. This is the purpose for the creation of Mensa; smart people are usually lonely.

Intelligent people are generally more cynical, as well. I'd like to say this is because the world is obviously fucked up and that smarter people realize this more intensely. A more reasonable answer, though, is because of the introverted nature of intelligent people.

Introversion leads a person to make fewer friends, as does the well-known nerd archetype that many geniuses carry with them.

Not being a member of society breeds resentment, fear, and anger towards society in general. This causes further introversion and subjectivity, which pushes society farther away from them, creating a vicious circle wherein the intelligent person holes up inside their own mind.

Geniuses are likely to feel rejected because they are smart, and social rejects are likely to think outside of the box just to spite society. The two are not inclusive, but go hand in hand in a lot of cases. The genius and the madman both create their own world, but who is remembered as a genius and who goes down as a madman depends on how many people they can convince to believe in their world.

Jesus was a genius and a madman, but people believed him and a paradigm was created. Same way with Einstein, Galileo, and, to a much less fantastic degree, one could even say Kurt Cobain. On the other hand, the part society does not like to examine, people like Charlie Manson have created fanatical cults and men like L. Ron Hubbard have created more reserved, but no less sinister, organizations behind a ridiculous conspiracy theory.