Why do some genius' become insane and are feared by the average?

I think that genius comes from the mind being overly stimulated, and certain types of people are not easily stimulated. It's possible that the reason these types of people don't get stimulated easily is because basic everyday life is unstimulating or negative events have caused the mind to shut off the ability to be stimulated.

For whatever reason if they are able to be stimulated by something (a strong reaction) they become over stimulated and behave in an "different" manner than the social norm-and normally people who appear both intelligent and different are naturally going to be feared.

If there is a situation like that i suppose, due to the praise of others they tend to have a pride which is not easily breakable. And they believe that everything they may do is correct, in which we can classify them as insane. Definitely, they are on different levels than genius, and i guess they are feared by the average due to the recognition genius's have, the average might not challenge them. They might think it is useless.