- Strengthen law enforcement through constant practice, and provide revenue to supporting companies
- Siphon money from one industry (drug trade) to help support the government and therefore support other industries that it feels are more beneficial to society
- Stigmatize unproductive habits, conditioning society to more productive/controlled behavior, incarcerating individuals who resist to make the society seem more productive overall
I'm sure there are many intentions that are well known that might overlap with what I'm suggesting, but I think the main point is that the war on drugs is not for the purpose that most people assume: to eliminate drugs from society. I think in a lot of ways it intentionally has the opposite effect. Also I think if society would have tolerated alcohol prohibition that the government would have been happy to keep that going as well for similar reasons.