I would suggest that there is no particularly good reason why the threshhold should be 0.08 instead of some other number. I know that the congresscritters in DC have spoken, and thus so mote it be, but Congress does many things that are unreasonable. If Congress hadn't passed the 0.08 legislation, what basis would you have for arguing for that particular figure?
"what basis would you have for arguing for that particular figure?"
The links I posted earlier in this thread.
Not to many disagree that impairment is pretty evident at .08. I think that .08 is pretty well established in testing studies and does show a level of impairment where elected officials can use them to deem .08 the accepted level where driving is no longer legal, much less safe.