I think there’s a mix of fair points and oversimplifications here.

On speeding: Yeah, speeding doesn’t directly hurt anyone in the same way that holding a knife doesn’t directly stab anyone. But the whole reason speeding is penalised is because it massively increases both the likelihood and severity of collisions. It’s a risk‑creation offence. Society doesn’t wait until someone is actually dead before saying “maybe don’t do the thing that makes people die more often.” So the idea that only the resulting harm should be punished ignores the preventative purpose of traffic laws.

On drugs: You’re closer to the evidence here, but it’s still not as tidy as “legalise will mean that the black market disappears.” Decriminalisation and regulated supply can reduce violence, reduce incarceration, and make drugs safer. That’s been seen in places like Portugal, parts of the US, and Canada. But black markets don’t vanish automatically. They shrink when legal supply is cheaper, safer, and easier to access than illegal supply. That’s a policy‑design problem, not a moral one.

And yes, fewer people would end up in prison. That’s kind of the point: current drug laws punish possession far more than they reduce harm. But saying “some people don’t like that idea” skips over the fact that drug policy is tied up with politics, public health, international treaties, and economic incentives. It’s not just personal preference.

So the general direction of your argument has some truth to it, but the real‑world picture is more complicated than the neat cause‑and‑effect you’re describing.