There is a bigger push for making marijuana legal in the United States today than at any previous time of my life (I'm thirty as of yesterday). It's not legal, of course, because the push to keep it illegal is also quite strong. And it's already illegal. It's easier to defend a fort than to storm it.
So let's assume, just for the sake of argument, that marijuana is actually immoral. It's evil, it's a sin, it makes baby Jesus twitch when he thinks about it. Even if I believed this, I still wouldn't push for the illegality of it.
From the standpoint of the real world, anti-marijuana laws are painfully ineffective. Rappers have pictures of themselves holding pot in their hands on their album covers and posters, not to mention videos on YouTube of them using it. There is an annual HempFest in Seattle, where people smoke pot openly, in full view of police. There are stores devoted entirely to marijuana paraphernalia here in the states, with the silly excuse that the items are for smoking tobacco. What exactly are your anti-marijuana laws accomplishing?
The problem is, most people think that the law should reflect what's right. If something is immoral, it should be illegal. If something is okay, don't worry about it. Besides the obvious issue that morals are essentially something that exist in our head, and they are different in different heads, there is the issue that laws don't stop things. They just make them more dangerous.
Let me say something unpopular: I don't like abortions. I think that, after a certain stage of development, fetuses shouldn't be intentionally killed. Sorry 'bout that. At the same time, though, I would be upset if the United States were to repeal Roe v. Wade. As much as I dislike legal abortions, I dislike illegal abortions twice as much. Taking away the clean and safe clinics, we would be pushing desperate teenage girls into an underground of unlicensed medicine, at huge risk.
Laws create undergrounds. If cigarettes were made illegal today, this time next year there would be tobacco kingpins warring with each other all over the country. Since cigarettes are sold at the supermarket, there are no cigarette dealers, no cigarette crackdowns, and no prisons filled with inmates who are in for cigarette-related charges.
We need to look at laws differently. Even if a piece of legislation disagrees with your moral compass, you have to realize that the law is not just a representation of right and wrong. Sometimes making something bad illegal makes the world a worse place, and you have to be strong enough to accept that the world we live in is more important than the righteousness of our laws.
Besides, a little pot never hurt anybody.