What an utterly bizarre notion!
Firstly, because it makes the laughable assumption that concert-goers live and act in a separate universe from the rest of us
Therefore, when they leave their concert and walk or drive home under the influence of their ‘tested’ drugs, when the crash their cars, or walk under buses, that will simply be for our wider society to sort out.
Also, what constitutes ‘safe’ drugs’? The effect of any drug is based entirely on the body chemistry and the experience of the person consuming it.
I take 10 mg of Citalopram a day. If I took 20mg, I would understand and be able to deal with the temporary effects. If my wife took 20 mg of the drug, she would be in bed for three days while the effects wore off.
My son in law likes a beer. He can drink four pints in an evening, and be perfectly social and lucid. I am tee-total, if I drank more than two pints I would be vomiting as a prelude to unconsciousness.
And as a final point, how long does the testing procedure take? Who pays for it?
This is PC right-on barminess and as usual it has not been thought through for a single moment.