12 penalty points ≠ ban

The issue would be then that people tend to rebel against laws that seem unfair, and disobey them.

It is important for the credibility of the drink drive law that it is seen to be reasonable - which broadly speaking it is at the moment.

Zero tolerance would possibly just create angry criminals out of previously reasonable people- the person who had two pints of weak lager shandy over a six hour evening out say.
And here we go again...why is it unfair to ask people to choose between consumption of alcohol, which affects your motor skills and reaction times, even at lower concentrations than the current limits, and the operation of heavy machinery on the public roads?