I'd be a lot more sanguine about busting people for DUI if the standard was still a scientifically set one. The reduction in driving ability at .08 vanishes into the noise of rest level, stress, other distractors, etc...
A legal .1 level is much less likely to be falsely diagnosed with a breathalyzer, avoid problems with people on chemo providing false positives*, etc...
*Read about a guy that, with a PROVEN 0.0 BAC, could blow a .08-.09 due to how his chemo and cancer interacted. He STILL had a hard time avoiding conviction because the state kept insisting that 'We've DECLARED the breathalyzer perfect, blowing a BAC of .08 after driving a vehicle is what's illegal, not driving drunk!!!'