*TLDR warning*
Yeah, it's an uncomfortable and tough job, but someone has to do it. I'm ultimately not ordered into duty to be people's friend; my non-evaluator peers love passing the buck on that, and lord knows I'm never in the "favorite IP" list as a result, ever.
Evaluating is actually rather easy to defend on the personality front, because you're a ghost in cold mic, so they can't accuse you of personality conflicts in the airplane. So this is more about the IP/non-evaluator role. To be clear, I'm not terse in the airplane, which is one of the more common complaints aggrieved students have against instructors. Their more common complaint I've faced is that I hold the line; they see it as "grading hard". They don't complain about it per se, they just try to tone-police you about misc grievances on the ground in order to lash out against you (meanie was late to the brief, he was too emphatic on the debrief, etc).
The uncomfortable reality is that some of my peers just don't want to grade to the line. Some don't really take this job seriously, which bothers me, but most within that cohort actually care but just don't want to lose their affability. Either way, they just expect those of us type-casted as "grim reapers" to act as safety nets/glovesaves and catch these weak swimmers before they're allowed to kill someone. I've been pigeonholed into that stereotype at work by now. Did I mention life ain't fair? But that's between me and my peers.
BL, I treat everybody with respect, and most importantly, I provide the same objective and neutral evaluation whether the guy is top stick or about to get washed out. Insufferably consistent line, and I'm proud of that. Not every baby turtle makes it to the ocean, and life ain't fair. Game here is Chess, it ain't checkers.