It's just not possible to legislate for the "reasonable man", who'll stop in for a pie and a pint on the way home.

Instead, we have to say that such and such a level of alcohol in the bloodstream is verboten, in order to get the message across that no, you can't drink 10 pints of wifebeater and be safely in control of a ton and a half of steel at 60 MPH, no matter how big your beer belly is.

Because the second case is what happens if you legislate thinking that people are going to be sensible and do the former.

Thank the fuckwits in society for our lowest-common-denominator approach to lawmaking.