this,it`s like the dark side in star wars.it`s power is addicting,it can devour youTheyre not necessarily insane...
Its comparable with a jinchuuriki, if they don't control the beast yet.
The more mentally unstable they get, the more dangerous they become
Uchiha principle is kinda the same, they become mentally unstable they develope a
natural counter measure.
I think the main problem with the uchiha is just, they learn how to achieve stronger powers
and build some kind of addiction to it, thus going in some sort of power wanting trance where
nothing is too much to do it.
My theory though