As I've just read in the news that Pat Robertson, of all people, has come out in favor of legalizing marijuana, I thought I would take a stab at the issue generally. There are many angles from which you could approach this issue: social, political, moral, medical, and even fiscal concerns come into the picture. While I think all of these are important, I want to stick with the moral/political side of things, because this is where our principles are really put to the test.
So here's the claim: drugs should be legalized, with certain regulations as necessary to prevent harm to those who are particularly vulnerable (such as children). Some positive arguments, as Robertson himself elucidates, include the following. First, it would reduce our prison population, saving us lots of money which we currently spend needlessly. Second, it would prevent violence in the form of "drug wars" between black market rivals or between drug dealers and police. Third, it would eliminate the rather obvious disparity in the legal system between wealthy drug users who find it easy to get away with and those in the lower class who are easy targets for police. Beyond these, legalization would probably also have a good effect on our economy, by creating more legitimate jobs, as unsavory as it might sound to most people.
Now let's deal with three objections. First, there's the paternalistic objection: shouldn't we save people from themselves? After all, drug addiction is pretty bad, and everyone hooked on drugs could use a little incentive to get off drugs. Do we really want to leave people alone while they ruin their lives, and possibly impose costs on the rest of us due to their poor health and poor decisions?
The answer to this is pretty clear: we don't need to make something illegal to help people stop doing it. On the contrary, it would probably be easier to help people quit their addictions if drug use were legal, since it would be easy for people to be out in the open about their use. If you want to be paternalistic, then let's have a compromise: instead of spending government funding on guns and prisons, let's spend it on rehab centers. Alcoholism is a real problem for many people, yet we don't arrest people for drinking. (We tried that before, it didn't turn out so well.) Or take smoking as an example: an entire industry has built up around helping people to quit, from nicotine patches to chewing gum.
A second objection has to do with law and order: aren't drug users more likely to be involved in other crimes? Well, let's weigh the moral merit of such an objection. Is it right to punish people for doing something they are going to do? Should I punish someone for using drugs because I think it will lead to violence? Again, take the issue of alcohol use. We punish people for drunk driving, but not for drinking. That's because drunk driving endangers lives, while drinking does not. But doesn't drinking lead to drunk driving? Well, in general, no. There is a pretty clear dividing line between the choice to use drugs in the privacy of your own home or private club, for example, and the choice to drive a two-ton piece of machinery down the road while intoxicated. One should not be punished because of bad associations between two distinct activities.
Thirdly, there is the following objection, related to the first two: won't legalization lead to more drug use, thereby degrading the morals of society? Some will answer this by pointing to studies that show eventual declines in drug use in countries where it has been legalized. However, let us make a more philosophical point in response to this objection. It is obvious that we cannot make illegal all things which are wrong. How can we possibly draw the line between things which should be legal and those which should be illegal?
To solve this puzzle, I propose the following test: is it peaceful? As someone with libertarian leanings, I believe that society must work first to be a peaceful society, and then we can focus on solving particular moral problems. Progress is best made through peace. When people feel coerced into abiding by a particular moral code, they tend to resent whoever assumes this moral authority over them. Within certain institutions such as the family, this can be a necessary and even healthy thing; but between existing communities of people, this is an unhealthy relationship which can only cause long-standing tension.
I have never used any drugs other than alcohol; I've never even smoked. But there really is virtue in tolerance, by which I mean permitting other people to do things you actually do not prefer. I grow increasingly discouraged that tolerance has fallen out of favor in our society; we seem to be forced to choose between endorsing or forbidding. If everything we find disgusting must be illegal, and likewise everything we make legal must be actively accepted as good, then our democracy will surely deteriorate (as it has done) into a tug of war, to which there is no end. I refuse to hold any stance on drug use other than tolerance: I think drug use is wrong, and I think it should be legal.
Simply ask yourself, do you really want men with guns locking someone away merely for possessing a substance which has certain negative effects on the human body when consumed? Does this punishment fit the crime? Perhaps a tax is a more fitting punishment; or, just maybe, the mere use of drugs is benign enough to simply be left alone, as are most activities done in private.