When most people argue against prohibition, they're not saying that making the bad thing available is great. They're saying that we can't effectively reduce the availability of things that people want, so when we attempt to do so, we end up with all of the negative externalities associated with prohibition without any of the actual prohibiting
This may be fine enough for weed, but what if harder drugs start being used 24% more? Even if they're in more pure form than from illegal sources, that doesn't sound like a net positive.
Another way of writing that headline is potentially "cannabis users 24% more likely to admit to using cannabis when in a state where it's legal", or even "marijuana legalization brings cannabis users from out of state".
Even if the study you're referring to does effectively control for those two factors- I would hesitate to apply those results to a harder drug like heroine. Marijuana education and legalization are happening at the same time. The information on Marijuana is pretty promising and education may incentivize it's use for some purposes. I do not believe the same about heroine- education would probably disincentivize it's use.
There's a whole lot of evidence that prohibition vs legalization each have negative effects and it is up to society to decide which is more appropriate in certain situations.
I doubt that food regulations are going to result in black market Doritos barons waging deadly turf wars in the streets. But I suspect it will result in food manufactures building a much worse product in response.