Bigred on the money. Salsa, I don't know what's got into you on this thread, YOU'RE NOT USUALLY LIKE THIS. Of course the limit has to be an arbitrary one! Everything's arbitrary! The only non-arbitrary limit would be zero! And of course it will be towards the lower end of the scale - if some people are impaired at (or even below) the limit, then we need to stop them driving while impaired.

The government and the law have a lot of dumb, unfair or disproportional rules we're expected to follow. Forbidding driving while impaired by alcohol is not one of them. I assume you've had some kind of run-in with the law? Drugs maybe? Fine, you have a genuine grievance, BUT NOT WITH THIS.