My first hand observations and understanding from working against, and layer with addicts; the first where they were a significant (though not necessarily majority) of people I dealt with in Loss Prevention, and then later worked with as part of a multi-disciplinary treatment team in an inpatient substance abuse and addictions program:
First, I don't subscribe to the theory that classical marijuana is a gateway drug; I call that form 'classical' because its often not what's on the street now, and therefore not what the newest studies are often based on when it comes to pot. It was long believed marijuana, unlike tobacco or alcohol, was not even physically addictive. Today the research has tended toward the other direction, but having taken some issue with the credibility of it due to the stuff often added before it hits the streets, as well as political motives tainting the findings.
One of the more common additives is methamphetamine. Methamphetamine is cheap to produce, extremely addictive, and often transparent to the user - even after smoking pot that's been cut with meth.
I therefore don't believe its a gateway drug, do believe its far less harmful than alcohol and tobacco (both legal), and further, as part of the growing acceptance within addictions of harm reduction strategies, favor decriminalizing it. Much better would be if the government were to legalize it, regulate it (thereby keeping the additives like meth out of it), and tax it. That income could then be used toward other substance abuse initiatives.
As to other illicit drugs, I don't favor any move toward legalization. I do favor diversion of end users away from the criminal justice system and into treatment; that said, my experience working with addicts has taught me that they do not stop unless the motivation comes from within somehow. Therefore a diversion program has to be aimed at motivating the addict to enter and complete rehab with some coercion, but of the carrot and stick variety. The carrot could be that if he enters rehab voluntarily, then criminal proceedings are stayed upon successful completion. The stick is that if he's discharged (voluntarily or otherwise), or fails to remain clean for some mandatory period, then he goes to court.
The mandatory period should be fairly short as too long is self-defeating, since a lengthy forced period of abstinence will seem insurmountable and is doomed to fail. The highest relapse rate occurs very early, therefore a more productive period might be just a week or two out of rehab. This also has to be a progressive system where punitive measures are introduced to ensure that he doesn't get his two weeks in clean and then relapses.
At any rate, I see the criminal justice role as a minor one for users as the bulk of effort and resources should be put toward education, rehabilitation, and sober living type programs and other forms of support for recovering addicts.
By taking the emphasis of criminalizing users, it not only frees up LE and justice system resources, it also, and most importantly, doesn't condemn them to live on crime, since a record for possession (without intent to distribute) dooms hundreds of thousands of people to live on the fringe, with very slim prospects for gainful employment. That as fact, and that as the knowledge that comes from a possession arrest now, creates a self-defeating cycle for them as people, and us as society who pay the price on many levels.
For trafficking, they need to stop wasting time and resources on petty pot traffickers and put the focus not only on dealers, but particularly on those who peddle to minors and those who sell harder drugs (which now is anything other than pot, though barring legalization the line is becoming more blurred as dealers increasingly add other substances to increase the high and create physical dependency).
Anyway that's my point of view, backed not only by education, but by experience in enforcement where I dealt with these individuals regularly when they committed theft, and later when I worked with them as part of an impatient treatment team where I followed not only the research, but most illuminating, had thousands of discussions with them about their backgrounds, attitudes and ambitions, lifestyle, and their own addiction from their point of view (history, usage, periods of abstinence or harm reduction, obstacles to recovery, etc).
As it stands now, the war on drugs is a total and complete failure of epic proportions. It will be regarded as such by future historians, and the approach has to change if any results are to come. Right now all it creates is a larger prison population (crime school), a snowballing problem that has done just that and still is doing that, and a massive tax payer drain and drain on society as a whole.
-Spyder