That's a dangerous approach. You cannot tell who has a drug problem based on first impressions, or even 50th impressions. Everyone should be allowed to do whatever drugs they choose on their OWN time.
Most drugs definitely have tells: physical signs like red eyes, sluggish or hyperactive movement, unusual behaviour like altered speech.
I'm not speaking in generalities. I know there are jobs out there that make no difference is the employee is high or not. But, there are also jobs where you can kill people if you are not safe. That's why it's not safe to say no company has the right to drug test. Of course they do! What if you kill somebody? I have no value on my own life, but I still respect the lives of people who want to to live...
Do I think people should drive on drugs? No, because a car can easily kill if not driven safely. Doesn't mean I think everybody who has a license should be regularly drug tested. Just pull them over if they appear unable to drive safely. When people drive drunk or stoned, it's fairly obvious.
I think targeting individuals and infringing on their rights should not be the first go to method to fix ills of society like drug abuse. Do I think there are some limited exceptions where drug testing might be warranted? Sure... but I definitely don't think it should be up to companies to decide what those exceptions are.
If you have a drug problem, it would be kind of you to have a job where your actions will not affect others lives in a serious way.
I do fly passenger airplanes and I like to take a
bonghit in the cockpit while flying through turbulence. But with modern autopilot these babies basically fly themselves so it's fine really... if I really need to pay attention I just snort some coke of the control panel to get focused again.