My framing of what you're saying here is that you could put on a DUI defense that consists of "I knew the risk, it was zero, and so whether or not I acted in conscious disregard of that risk, I was not reckless."

I'm struggling to see how you could truly analyze the additional risk of being > .08 as zero but 1) I expect you're about to make an example and 2) I reckon the example is out there.

A one foot journey on a flat road during the day in good weather seems a bit degenerate, no?

Your "at what point is that a rationale for incarceration based on risk alone" reminds me a little of banning fireworks. We're not banning fireworks because we hate fun, we're banning them because of the risk of a deleterious effect that is not possible without an explosive. Do we incarcerate for fireworks possession? We usually do not. This is a thing that is worth thinking about.

I guess you could say we're not imprisoning because of the risk; we're imprisoning because drunk drivers are unable to follow a very bright line rule. Why would I be imprisoned for driving 180 mph? Same reason.