I can agree with that. I'd bet a majority, perhaps a vast majority, of all alchol related deaths don't happen because the driver had impaired reflexes, but because they were reckless. There is no breathilizer for 'gumption'. :)
But, I'm not sure how to settle the paradox of this individual variation in order to fairly define a DUI, as laws cannot really be written that way (unless an objective reflex test or something was developed)... now that would be interesting... :)
I'm not one to get hot and bothered over our current DUI laws, sure some might be a bit unfair to certain individuals, and too lienent to others, but I'm not sure how you change the system to make it 'fair' and there are plenty of more important things to put one's time and energy into fighting...
For one thing, abolish "sobriety checkpoints". The whole premise behind them is absurd: stop vehicles randomly on the hopes that one stumbles upon a drunk driver (well, that's the most charitable explanation). It would be much more effective (and much less of an attack on sober people) for officers to look for people who seem unable to drive their vehicles smoothly and effectively. Sure, sometimes perfectly sober people will get pulled over (I got pulled over shortly after getting my learner's permit, the first time I was driving a stickshift car; officer probably thought I was drunk until he saw the permit, said 'first time driving stick?', and I answered in the affirmative) but officers could probably get more of the dangerous drunks off the road by doing that than by wasting time harassing sober drivers.
Of course, for all this to really work, police cars should be equipped with video. Given the extent to which prices have fallen, I can't see much excuse for not doing so (except that juries might decide they didn't agree with officers' actions...)