You are confusing an individuals personal problems with side effects of marijuana. Correlation not causation. He obviously has other issues and used marijuana as a crutch. What you need to understand is the difference between a mental crutch or addiction and a physical one. Mentally anything can be addicted to or be used as a crutch for ones personal problems. The object/action itself may not cause such behaviors but it is attached to these things by the specific people that us them and the object/action itself is not attaching these behaviors to people. A physical addiction is something that causes physical withdrawals and the object or action is the cause of such affects. What you are describing of your friend fits snuggly into mental addiction. He was simply using marijuana as a crutch to escape his problems however his behavior was not caused by the marijuana itself. He could have just as easily hidden under other addictions like videos games or sex.