This attitude is a bit ignorant, and seems to indicate that you've never used marijuana, or while using never had a thought deeper than, "I'm hungry, man!"
I've come into contact with such a variety of people who use marijuana in a plethora of different ways, I would have never believed it. People in all different walks of life-- lawyers, doctors, teachers, writers, musicians, tour guides, Israeli soldiers...successful people, unsuccessful people, lazy people, energetic people, you name it.
If used in moderation, there's no reason why marijuana can't be a part of a well-rounded life.
Your views are about 50 years out of date, in my opinion.