Plent of folks in desk jobs are doing it for their own personal reasons. Obviously they cannot be vocal union agitators in and around the HQ building, but that doesn't mean they don't support the union and vote accordingly. Including most instructors.

Obviously those who are bucking for upward mobility, even into the executive ranks, are cut from a different mold altogether.

But maybe this is airline specific... out of the three where I had any SA into such things the majority of instructors have always been fine, about half the base CP's have been great or good, and the vast majority of non-leadership staff have been fine. The latter just do their job and rarely have much direct authority over pilots... worts they usually do is random, ill-conceived SOP revisions. But even so it's better to have line pilots doing those jobs, as opposed to retired pilots, pilots out on medical from other airlines, or non-pilots.