I think it's the fallacy of the breath test in full flow. One man can drink 3 pints and be over the limit, but feel capable and probably is, then someone like yourself can sniff a shandy, get behind the wheel and then mow dow a load of school children on a field trip while still under the limit.
Not to diss the breath test though. There has to be a mechanism in place and it does the job for the most part.
