No one disagrees that intoxication on the job should not and cannot be tolerated. But the issue of drug testing, as a practical matter, impacts whether an employee - who may capably and soberly perform the tasks of his job every day - can enjoy a drink or a toke while off-duty in the privacy of his home. Yes, I understand that an employer has the right, but it seems wrong somehow that an employer can fire an employee for harmless activity on the weekends.
It is a condition of employment. If you don't like it, don't work there.
If you still have enough alcohol in your system when you go to work to violate those conditions, you are a menace in those work environments. For CDL drivers and airline pilots, for example, that level is a fraction of the DUI level. While no one has yet succeeded in quantifying what levels of cannabanoids present indicate residual impairment, most of the companies I have worked for have zero tolerance simply because that is an easy standard to measure, and cannabis is illegal in those states anyway.
If you can't exercise self-restraint and good judgement in that part of your personal life, what is there to make an employer believe that you will exercise self-restraint or good judgement on their behalf? Add to that the incredible liability aspects of some jobs, and the employer places expectations on an employee as a condition of continued employment.
Would you want someone under the influence (even residually), flying the plane, driving the bus, running the oil rig, on the throttle of the commuter train, operating the nuclear power plant, just to name a few?
There are plenty of jobs which won't get anyone hurt, create an environmental disaster, or wreck expensive equipment you can do, where the employer doesn't test their employees.
