2) (okay not so easy apparently) enforce laws against stealing and assault.

Also investigate what are the root causes of this behavior. Marijuana is not addictive on nearly the level of other substances, for most people. It seems to me that barring exceptional cases, someone must be coming from a very bad place if the best way they can find to spend their time is to commit crimes - that will likely land them in jail later if not sooner - just so they can smoke pot.

Massachusetts de-criminalized possession of small quanitities of pot years ago (meaning the possessor is not likely a dealer). I know of zero problems.