I like the word impaired, basically because it doesn't really mean anything. People can be impaired for many reasons. I'm sure we've all driven in cars behind either old folks or new drivers, who may well be impaired due to age or lack of ability. Would an experienced driver of middle age be more impaired with a pint or two compared to a new driver who has never driven down a certain city centre route? Surely the driver who has had a drink would be more impaired than had he not had a drink if we were to compare himself to himself, however, it's never that easy. I have flown with pilots who have been more detrimental to the operation just by being on the flight deck, let alone if they had had a pint or two. I suppose our operation was impaired.
In no way do I condone drinking prior to flying. It will always be wrong. You will indeed be impaired, compared to your own previous ability. However, an arbitrary alcohol reading will not be a simple judgement of impairment. Lack of sleep is a huge impairment. How do you compare a junior pilot with only a few hours of sleep compared to a senior Captain with two glasses of wine under his belt 8 hours before sign on? Food for thought. Or maybe not.