There is one difference between first responders/doctors and the other classes (and the moderators under discussion here)

First responders/doctors/CPS investigators see the worst but they also have days where they make a difference. Save a life or multiple lives. I'm sure it's a huge part of what makes the job bearable, and to some meaningful.

I'm not discounting your point about high rates of suicide either. If anything, when you take away any good days, you're left, as a content moderator, with just seeing the worst of the world day in, day out, with nothing to make it meaningful. I'd suggest that's something we as a society should not tolerate as being an acceptable trade for the ability to share cat photos.