I will concur that it isn't addictive in the physical sense like nicotine or coke.
But I know a lot of people that can't seem to quit smoking it...and I don't mean an occasional joint, I mean the people that get up in the morning for the specific purpose of getting high.
Those people definitely have problems. Take away the pot and they'd find some other substance or activity to obsess on. I don't believe in penalizing everyone for the sake of the few who are having problems.