So let me get this straight; they decriminalized buying it but not selling it. Sorry, but that sounds goofy as hell. And I think they just set themselves up for a huge, new criminal enterprise to setup shop in Mass.
There was already a huge criminal operation supplying pot to people in Massachusetts, just like everywhere else. They didn't legalize possession, they just decriminalized it. It's still against the law. They're just going to write tickets now instead of wasting time taking people in for nothing other than pot. Several states have already decriminalized simple possession of pot and if you look at the pot use statistics for the states you'll see that states that have decriminalized have similar per capita pot use rates to the rest of the country. It doesn't really make a difference in the number of people who will smoke pot.
Think about it. Most pot smokers never get caught. As long as they are reasonably careful, the chance that they'll get caught is minuscule. They're transactions where they buy their pot are behind closed doors, most of the smoking is down behind closed doors. No doubt better than 99.9% of the time if a “pot smoking” has occurred the police know nothing about it. Those daily and near daily pot smokers who smoke for years will do it thousands of times and most of them will never get caught. And if they do get caught, it's not the end of the world. It's a misdemeanor. In all likelihood they won't get a jail sentence. They'll basically get a slap on the wrist, and even in states where it is not decriminalized often it's possible to keep it off your record or at least be able to get it expunged in a year or so. I'm a lawyer in the South in a state where they are pretty hard on people for drug crimes but most of the time if I have a client with a marijuana arrest I'm going to be able to work something out that keeps the conviction off his record, or at a minimum I'll get it such that it can be easily expunged if after court he stays out of trouble for a year, sometimes less. He'll pay a fine and have to spend Saturday morning watching anti-pot films and might have to report to a probation officer a few times, but that's it. The far remote possibility of getting caught and getting what is basically a slap on the wrist can't be much more of a deterrent than the far remote possibility of getting caught and having to pay a small fine. One is a little more of a nuisance than the other but the chance of getting caught is so slight that people don't really care. If you are one of the few who wants to smoke pot but won't because of the remote possibility of getting caught and getting arrested and getting what is basically a slap on the wrist, you're probably going to be deterred by the remote possibility of getting caught and getting a ticket for it too. There really is little difference in the deterrent effect of the laws in states that have decriminalized and those that have not, as is clearly evidenced by the lack of difference in the per capita percentage of those who use marijuana in states that have decriminalized compared to those that have not.