No, it's a bad analogy because excessive speeding, in and of itself, places others in direct jeopardy, while drug use, in and of itself, does not place others in direct jeopardy. Therefore, it is a bad analogy.
A speeding car is potential energy,
No, that's kinetic energy. Potential energy is when it's at a high altitude, and could fall (and therefore gain kinetic energy) but it hasn't yet - which is why it's "potential" energy. But, enough of elementary school science for today.
The analogy is perfect because to you there is nothing wrong in the chain of events until the final step.
What is the corresponding "final step" when someone is smoking a joint, since you're so enamored of your analogy?
Thus, how can you say that someone that is speeding is reckless? They haven't caused an accident yet have they? You just refuse to apply the same logic to drug use. Its exactly the same thing.
Because a drug user is an armed-robber-in-waiting? Bigot. The same argument as "all black people are rapists-in-waiting" and "all gun owners are school shooters in waiting".
excessive speeding, in and of itself, places others in direct jeopardy
How? Who are you to say what the speed limit should be? You could only base this on the fact that a higher percentage of speeders commit crimes than nonspeeders. You are a tyrant by your own definition. It remains the perfect analogy.
Only using statistics, which is what is used to determine speed limits in relation to accidents. How this can be above anyone's comprehension is startling. Can you find the United States on a map of North America?