It’d be hard to convince a jury beyond a reasonable doubt that you intended to distribute beers from a 12 pack.

Only because most jurors have some background knowledge of what constitutes a "normal" amount of beer to buy and consume. A gram of cocaine could be described as 6 lines, or it could be called several dozen bumps. The prosecution is going to go up there and wax poetic about how you'd only buy multiple thirtyracks if you're planning on throwing a party i.e. distributing, and your average jury will eat that up.

Assuming you even get to a jury trial. For most pseudo-distribution cases like this, the defendant is going to plead out, because they know they're dead to rights on the possession charge, and if the judge throws the book at them for that then they may well have been better off taking the distribution plea deal.

This varies a lot by jurisdiction so it’s hard to determine aggregate impacts. For every anecdote of judges throwing the book at someone, I could probably offer one of judges letting off someone easy. The important point stands regardless: Sweden has a larger percent of its prison population incarcerated for drug offenses than the United States. Most people going to prison were convicted of a violent crime.

Sorry, maybe I was unclear: the potentially high penalties for possession are used a threat, to push people into pleading guilty on the distribution charges. Possession alone can potentially land you in jail for up to 3 years. Distribution has a wider range, from 1 year up to potentially 9 years.

If you're caught in possession of a couple grams of coke, then the prosecutor is going to want to get you on distribution. They can say something like "You will be found guilty of possession, we both know that. If you plead guilty on both counts, we can recommend concurrent sentencing and you'll be out of prison in less than two years. If you don't take the deal, we're going to push for everything we can get: even if you get off on the distribution charge, you'll still be in prison for 3 years for possession."

Now, you or I, affluent tech-bros that this forum attracts, know that this is a terrible deal. We'd hire a lawyer, fight it tooth and nail, and walk away with a possession conviction and a slap on the wrist sentence. But if you're some broke kid, with a public defender who's really just there to counsel you on what plea deal you should take, it might not seem like such a bad idea.

I understand how pre-trial negotiations work, and I am not an affluent tech bro. In fact, I spent some time consulting DA offices throughout the country on how to adopt best practices in criminal justice reform. Public defenders are not universally pushovers and judges and juries are not universally looking for blood.

Like I said, getting aggregate statistics on how pleading down impacts the composition of the prison population is very hard, but the fact of the matter is most people who end up in prison don’t do so because of anything which looks like only recreational drug use.