Scott, I'm sure those things happen to people who never partake at all. Smoking pot doesn't turn anyone into something that they already aren't or already are. People don't become murderers or rapists "after" smoking pot. The assumption that they do is profoundly ridiculous.
Even people under the influence of opiate narcotics seldom become violent. In fact, people using opiates tend to express feelings of calmness. It's reported that Keats penned his greatest poetry while using opium.
In all fairness while evaluating the dangers of drugs, I'd say that alcohol is the one drug that turns people violent and gives them balls of brass. Marijuana tends to mellow people out and make them hungry. I've never seen it aggravate violent tendencies. Alcohol amplifies happiness, sadness or anger. Opiates and marijuana tend to have a calming effect. If a philosopher smokes pot, they don't become more philosophical. They "might" become philosophical in a different way, but they were already a philosopher.
Here indeed is the unknown quantity among narcotics. No one can predict its effect. No one knows, when he places a marijuana cigarette to his lips, whether he will become a philosopher, a joyous reveler in a musical heaven, a mad insensate, a calm philosopher, or a murderer.