First let me say, I do not use marijuana, I do not encourage the use of marijuana. But I don't see why nonviolent voluntary interactions between people should result in prison for the parties involved.
Questions to consider.
1, Is the use of marijuana morally wrong in general?
2. Is the use of marijuana morally wrong because statutes and ordinances say it is unlawful to posses it?
3. Would America erupt into a lawless waist land if marijuana was decriminalized tomorrow?(ever been to Amsterdam?)
4. Does the use of marijuana hurt more people yearly than alcohol(remember prohibition)?
5. Does the use of marijuana kill more people yearly than officers(and SWAT) doing drug raids?
6. Do you believe that people should be put in danger of being killed when they have injured or potentially injured anyone?
As for the criminal element of marijuana, cracking down on the selling of marijuana raises the profits of the remaining sellers, with high profits more people want to get in on the profits so they start selling witch begins turf wars between sellers trying to maintain a monopoly with artificially high profit levels.
So decrease supply, then the relative demand of the supply on the market goes up. demand goes up, profits go up. more profit, more people trying to make a profit.
7. What do you fear?
The Game?

8. should any goods or services be provided to customers at the barrel of a gun?
I want people out there to answer a few of these questions.
I also will be fine with people calling me a hippie for posting this, I kinda expect it.