I can see a few downsides to legalization, but I would think most are only applicable to California. For one, you turn the sales over to the government which can be good for revenue, but bad for users as it's gonna be taxed like shit. My brother who moved to from Cali to Colorado about a year ago always bitches how he pays twice what he used to. People always rebuttle with "competition will drive prices down", and that very well may be the case and may be happening as we speak (It's not in my brothers area, but I can't speak for all legalized states), but has competition drove down the price of alcohol or cigarettes? I assume price will flatline and even start to rise as tax increases.
Another is that it's likely the smoking age will be raised to 21 years old (from California's any age, as long as children have parents approval). While this doesn't affect me it will affect many I know, and I think at 18 years old your more than responsible enough to handle purchasing and consuming pot. Something else that I fear is unwanted media attention on certain products. If full legalization is set in were gonna have parents bitching about how these products are "too strong for the children' and this will likely lead to restrictions on cannabis products...
Keep in mind this is coming from somewhere with probably the most crooked medical system in all of the US, where all it takes is 5 minutes to "discuss" a fake ailment with the equivalent of a doctor with a loose hand to get a recommendation to cheap, potent cannabis so what affects me may be a bit selfish to the rest of the country.
If medical can co-exist with legalization you would think that would solve things, but then again now the government will be in charge of this as well and the system won't be so "lenient". I should say I do have legitimate ailments to aquire cannabis, but I'd be lying if I said I don't think things are okay as of now (with the exception of DEA raids). As of now it is essentially legal over here only everything is in the hands of the people, and I prefer it stay that way...
With that said I don't think I could care any less about "the average joe" having access to potent cannabis though, good weed is always gonna be around and for almost the last decade good weed has been easier to find than stress/schwagg/brick whatever it's called in your location... and this trend is only growing. It's about time we stop buying piss weed from the cartels anyways, get that poop weed out of here for good and at least bring in low grade buds that require examination before re-sale for those who prefer a more mild smoke.
All dispenaries I've been to also stock lower grades of bud as well as high CBD low THC buds, extracts, and concentrates so if joe schmoe finds top shelf too much there's always an alternative. If someone can't handle responsible use then that's no one's fault but their own. Should we restrict vodka for those who can't drink responsibly? What about cigars for those who can't control their smoking habit? I can also think of a few positives to legalization, but this post has droned on long enough.