People are cheap and corrupt. The speed bump this presents is real, but minor, in the face of a couple medical shops looking to save $100/pop on a dozen monitors.

I hope it's rare, but I think a persistent nag window ("Your display isn't calibrated and may not be accurate") is probably a better answer than refusing to work altogether, because it will be clear about the source of the problem and less likely to get nailed down.

You have to draw a line somewhere, I guess. As far as I remember, protections against accidental misuse and foreseeable abuse of a device are required in medical equipment. But malicious circumvention of protections or any kind of active tampering are a whole other category in my opinion.

Medical devices are insanely expensive (a CT scanner may reach a million dollars), you won’t risk $100 on such a small thing as a screen.