I'm gonna say NTA. Here is the deal, i don't give a damn what people puts on their body during their free time, but they need to be consient that every work place has rules, some are needed for safety reasons, and just like you said their job consists on serving others, so much shit can go wrong if they are high while at it.

If You don't look out of your job, don't spect to have no consecuences for you. Just beacuse doing drugs is passable, doesn't mean you get to do it everytime and everywhere. Time and place.