> There certainly have been a few times when I was expecting to drive but clearly wasn't fit to and had to make other arrangements.

My example (and experience) wasn't about starting to drive. It was about being 4 hours into a 7-8 hour drive. The slow degradation of attention while sitting in a static position while watching static scenery go by for hours at a time.

> And, in the gentlest possible way, if you were unable to recognize that you were so tired that you were likely to fall asleep while driving and make another choice, you were demonstrably unfit to drive at that time.

Part of being unfit is sometimes not easily recognizing you're unfit. If you start in a perfectly fine shape, but degrade slowly over time, it can be hard to note the exact moment when things have gotten to a point where you should stop. And the whole point of my post was that recognizing this point, especially if it's over time and a slow degradation, can be hard if you've never experienced it before.

> I can't argue rationally against such an irresponsible and selfish position

Well, I don't think the people in this little corner of the discussion it are arguing that. People definitely shouldn't drive while impaired. I just think we should also consider, and see if there's a way to help, people that don't have enough experience to know when they're flirting with that state, for whatever reason it may be. Hopefully that at least some people here aren't arguing for allowing impaired people to drive is some consolation and reduces your stress at least a little. :/