Marijuana is a terrible idea to use generally. Some people use it with more pleasure than harm, but that's true of heroin too (which is much worse generally).
I've long said, we should investigate the effect of legalizing Marijuana, and consider it. I lean towards doing so.
We should have anti-Marijuana use educational campaigns about the harmful effects, similar to how we do with Cigarettes, and whatever resources are helpful to quit it.
The shifting of the billions of dollars now going to criminal organizations, leading to a lot of violence and other criminal organizations being well funded, the reduction in law enforcement and prison costs, the current prisoners being (presumably) more humanely out of prison and paying taxes, and the movement of the product to legitimate employment and taxation, are benefits that seem to greatly outweigh any benefits of the ban.
The main thing in the way seems to be politicians worried about voter reaction.