I think you're logically correct. It's the feeling such a policy elicits which makes it untenable. I agree with your points conceptually, but the moment I would have to install a government speed limiter on my car is the moment I vote for someone else. It feels invasive, and I don't like feeling like the paternal hand of the government is all the way up my ass, controlling my gas pedal.
I'm sure the "chronic shit driver, bad enough to have a judge mandate a speed limiter" vote is a big block that politicians will be lining up to appease. Just like the "chronic drunk driver, bad enough to have a judge mandate an interlock" bloc.
