It is, however, really the only alternative to legalization.

Decriminalization is stupid. Dispensary systems are stupid. Coffee shops are stupid.

Decriminalization is stupid because the implication is that cannabis is evil, and the only reason people want to smoke it is that they're addicted. This is false. The "push toward treatment" isn't helpful for anyone who isn't addicted and doesn't want to be treated, like me. Plus there's the implication that selling someone to someone who asks for it is somehow evil, which is even worse ("Selling is legal! Fucking is legal! Why isn't selling fucking legal?!").

Dispensary systems are stupid because dishonesty is baked (haha) into the system. The South Park episode Medicinal Fried Chicken is a decent explanation, but the short of it is that people fake illness to get weed. Granted, this is like people faking illness to get painkillers -- but since cannabis is significantly safer than opioids and benzodiazepines, doctors are significantly less likely to care. It's not an issue with physical consequences, since cannabis is extremely safe when used under medical supervision, just the fact that lying becomes so much more prevalent.

Coffee shops are lame because free markets work[1], so why don't we have one? They're not that bad, though -- the implementation of such a system would bump the legalization of cannabis way down my priority list.

What really gets me on this is that people conflate the
question "should cannabis be legal" with the question "should you smoke cannabis". Nobody conflates the legality of trampolines with the safety of trampolines. I find it incredibly disheartening when people I know -- smart people, in most respects -- respond to legalization with the idiotic knee-jerks "but it's dangerous!", "but my friend does nothing but smoke weed", ad absurdum. I know people who do nothing but play video games. I know at least one person who quit his job and left everyone he knew to become a paragliding instructor. He took a huge pay cut, too. And this latter example, I think, illustrates the biggest issue I have with arguments like yours:

Who the hell do you think you are that you can dictate what someone does with their life? If it's what they enjoy, they can go for it. Even if it is a bad decision -- you really can't outlaw bad decisions, because it's hard to say what is a bad decision. Thing is, the sort of "always-on" lifestyle, that sort where cannabis (also other distracting activities) is most likely to interfere, really isn't a good fit for some people. Some people burn out on weed, some burn out on other things.

Thing is, sometimes people just burn out. I think there are a lot of people who come into this argument from a pro-prohibition point of view because someone close to them changed after they started smoking marijuana. And I think that this is akin to blaming a spark for a bomb. The thing is, that your stock-broker friend may in fact have been unhappy as a stock broker. It is possible, even likely, from my anecdotal experience, that he latched onto weed because he didn't like where he was in life. It doesn't really matter if you think he should have liked where he was in life.

There are plenty of harm reduction arguments for legalization, but I prefer the libertarian argument because, I think, it most directly refutes the central point of the popular anti-legalization arguments.

[1]: with a few exceptions.