Ok, im not going to flat out disagree with you that pot is not bad, because for some people it is, but you should not paint everyone with the same brush, because all people are different. It sounds like your brother has some underlying issues that would be there with or with-out the pot, and that the drug usage is just a symptom, but I'm not a doctor so I can't say for sure.
I don't really like pot, I think its a waste of money, it stinks, and it makes people less interesting to hang out with (when they're stoned anyway) -- However, not everyone reacts the same to it, I know some people who totally vegitate while they're stoned and others who act kinda hyper. It all depends on your personality and brain chemistry. Obviously, your brothers brain chemistry is fvcked. That doesn't mean pot is bad, that means your brother shouldn't be smoking it.