Addiction potential is heavily tied to one's circumstances. The more desperate the circumstances, the greater the abuse potential. For example, you specifically listed crack as opposed to run of the mill powder cocaine. The only difference between them from an abuse potential perspective is the purchasing power of the user. Likewise, the raver who's popping some mystery mix of amphetamine, methamphetamine, and MDMA at a party once a month is far less likely to succumb to addiction than poor sap living in Redding where the only thing available for entertainment is smoking meth. Opiates are self-selecting in this regard: they're not that pleasant relative to other drugs, except for their ability to make you content, which only really appeals to the desperate.

If we follow your "it's illegal because there's a probability" theory of law enforcement, then it should only be illegal to do drugs while poor, which is pretty much where the law stands today without the deceptive veneer of equality. Now, that should sound like an absurd legal take, because it is. The reasonable response is that it's poverty that's the problem, and it's not a problem we solve by throwing all the poor people in jail.

The irony? The more impoverished people we incarcerate, the more the social fabric is stretched and torn. That is, the more poverty persists.

The Poverty Industrial Complex (i.e., law enforcement, gov agencies, non-profits) is quite content with a persistence of the status quo.

I think we’d do better at solving problems with these drugs if treated the user as the primary victim as opposed to the perpetrator of the crime.

"some substances simply cannot be used safely for recreation."

Do you have hard data on this? Because otherwise you are creating lots of victims with the war on drugs, who would otherwise just use drugs recreational without harming anyone.

In the medical world, this is typically quantified by the Therapeutic Index[1], which is basically how much margin there is between an effective (therapeutic) dose and a lethal dose. (Fentanyl and heroin have notoriously thin margins, while cannabis is famously wide.)

It's a big consideration in what's OTC vs Rx, and what guardrails (inpatient only, regular blood draws, etc) are needed.

There was a good "magic quadrant"-style plot of this against addictive potential, but I can't seem to find it just yet. (This [2] is close.)

It doesn't consider externalities, so it's not great for the "do drugs and you'll end up unemployed, and if you're unemployed you'll end up homeless, and homeless people are a cost on the community" class of arguments.

  [1] https://en.wikipedia.org/wiki/Therapeutic_index

  [2] https://en.m.wikipedia.org/wiki/File:Rational_scale_to_assess_the_harm_of_drugs_%28mean_physical_harm_and_mean_dependence%29.svg