Old_Geezer - "Your body produces alcohol andy, so are we all to be banned ?"
I would suggest that it is in such miniscule amounts as to be unmeasureable, so maybe you are simply looking for a diversion of the thread - ?
"I think complete abstinence whilst intending to drive is not a reasonable expectation, as proven by the many who don't adhere to that extreme."
Why not? It's not compulsory to ingest alcohol and drive a car, it can be done without - and in the interests of road safety, in my view, is should be.
"And indeed it is over the top anyway. Lots of things increase risk, but we don't ban them all: the important thing is not to be irresponsible about it."
We will have to disagree then - I regard the notion of Rusian Roulette with a breathalyser as supremely irresponsible.
"Our present legal limit is about right. You can have one or two with your meal and still be permitted to drive safely home."
Not so - if I had 'one or two' i would be swerving all over the road. Are we to suggest that only hardened drinkers who can build up a tolerence of alcohol should be able to drink and drive? What about the eighteenth birthday drinker who passed his test the day before and is having a double celebration - his first drink and his first drive solo? Does that sound like someone who 'drive safely home'?
It is purely because the variables in terms of tolerance and circumstances are so vast that a zero tolerance cuts out any doubt about where the law stands - if you drink, you don't drive, and vice versa.
I can't see what's difficult about that - but I can see why society wilfully refuses to accept it as a potential for legislation - for the reasons I outlined in my first post.