[Margaret Pilkington]

You say you get it, and you provide a very valid argument as to why it is unsafe for people to be in a work environment under the influence, but then in the next breath you ask if it should be employers 'policing' their staff.

They are not policing their staff, they are just ensuring that the work environment is safe from preventable hazards......and they have a legal,responsibility to do this. They have to have public liability insurance, and this has to be displayed so that all and sundry can see that is current and up to date.
Employers have lots of legal responsibilities. By ensuring their staff come to work in a fit state they are ensuring they do not get stung for damages if something does go wrong.
To answer your last question.....what kind of world are we living in?
Well, you have eyes and ears.....you see the same things that I see.....we are living in an increasingly dangerous and litiginous world, where lawyers tell,people 'no win, no fee'.