I think it should be part of your driving test....take the test sober, after 2 drinks, 4 drinks, 8 drinks, etc LOL. Some people can drive good after some drinks and some can't drive to begin with. I have friends who's cars I'd rather be a passenger in after they've drank 10 beers than other friends dead sober.
It's just like any other traffic law....it's a big blanket trying to stop a few idiots who can't handle themselves. Me going 10, 20, or 30 over the speed limit on a nice piece of deserted highway ain't hurting anyone, but I'll still get the ticket just the same as someone speeding through a school zone at lunch hour.