I also think a big factor is what kind of equipment we're talking about. If you expect the equipment's value to be impacted by the use, as your "my gear isn't there for them to joyride" comment touches on, this is a bigger issue. I would never use my personal computer (or expensive camera equipment) for work without some sort of compensation because that usage implies a certain amount of deterioration (physical wear/damage) and/or compromise (corporate software/policies imposed on my machine). This seems pretty negligible for a monitor.
I'm confused what you were disagreeing with me about then tbh. Sure you can argue a monitor doesn't rise to that level but clearly we agree that there is some line here, even if we don't agree on where it is.
Was I disagreeing with you? I don't think so. I was just making a distinction between the use cases since you objected to the monitor purchase by comparing it to the use of your camera.
