I have no problems with fairness of 'zero tolerance' for detectable THC, other drugs, nutritional supplements, etc. as long as the rules are clear, can be followed by everyone, everyone must follow these same rules and the tests themselves are accurate. Many professions have their own stupid rules about drugs and other things.
But these and a lot of other similar testing rules are often just stupid - always skewed towards zero detection, maximal enforcement, with now-detectable but unintentional/accidental exposure to totally insignificant amounts enough to "fail" testing. They should at least allow CBD use and along with that some biologically insignificant but chemically detectable levels of THC allowed, whether presumed from the CBD or unintentional smoke/vapor or edible (food contamination) intake.