So? Random drug tests required by government agencies and schools are clearly constitutional (besides being extremely useful), and courts have almost invariably upheld them. Such was the case here. If some ACLU type had managed to get a background check policy struck down, and Mister Kindly with the "loving touch" was a pedophile rather than a potential pothead, folks on this forum would be the first ones to squeal. If you won't do what your employer legally wants you to do, it's twenty-three skidoo, Gramps!
That's pretty much my point... you're not going to find out who's a child molestor or otherwise dangerous to children through a drug test. And there may be some very good personnel who will fail those tests that you wouldn't want to fire.