Many assumptions in this thread, but I know from personal experience that disturbed people who smoke pot (or drink for that matter) can act and appear psychotic.
Marijuana causes psychosis in one form or another. It creates paranoia and attacks the central nervous system. Some people appear more affected than others, but it is a very harmful psychedelic drug.
Having said that, however, I have to add that I've recently changed my mind and now believe that laws making drugs illegal do more harm than good and should be done away with.
http://www.youtube.com/watch?v=nLsCC0LZxkY