For me, the crux of the question is the statement that their workplaces have taken all reasonable measures to protect their staff.
I wouldn't consider the fear or anxiety about COVID to be the primary consideration - rather, is that fear or anxiety justified? In your medical opinion, do the measures taken in the workplace actually protect staff, or are they just the things that can be reasonably done to partly reduce the risk while still leaving staff exposed to an unacceptable hazard? Just because reasonable efforts have been taken, that doesn't mean it's safe. If you believe the people will be just as safe at work as at home, and they just don't want to go to work because they are frightened of something that isn't really a threat, then I would think that is insufficient. If the threat is still significant, but is simply less than it would be with no measures at all, then I could see justification for saying they should be able to stay home.
I recall looking over the pandemic staffing plan of a previous agency I worked for many years ago, as part of my emergency prep work (yes, they did actually have one!). Their plan was to divide the staff into three groups, and to use just the first group for a couple weeks (with extensive overtime and cross-staffing) to reduce how many people were exposed at once. Then, when that group became so sick they could no longer function, they would be sent home and the next group called in. That would then be done again, and the assumption was that by the time the third group was so sick they couldn't work, the survivors of the first group could be brought back in again for another cycle. In the agency's mind, it was a great plan - it ensured work functions were being completed, it maximized operational continuity, it had a timeline reasoned out... but they gave not a single thought in the world for the fact that their workers are actual humans and might not be ok with the idea of being expendable OT plague machines. It is important to know what the measures an employer has in place actually do, and who they are "reasonable" for.