Do other people get this response when attempting to validate? Let's say the other person is complaining about X and you say "it sounds like you feel this is unfair [or some other descriptive]" and their response is to get angrier and say "it doesn't FEEL unfair! It IS unfair!" And how do you respond?
Here's the thing, this is a double-edged sword so we really need more context.
I can remember talking to my two daughters as teens (one BPD, one normal) and saying, "Hey, there's a new water park about an hour away and I'd like to go this Saturday. So if you get your rooms cleaned up before then and knock out all your homework, we'll leave early Saturday morning.
My non-BPD kid would race upstairs and clean her room immediately- and I'm talking about cleaning her closet, vacuuming the whole nine yards. The BPD kid would appear uninterested and do everything but clean her room. Sometimes she'd throw stuff around to make her room worse.
So the days would pass...Wednesday, Thursday, Friday. One room is spotless. The other is a disaster. And I'd say, "I'm leaving tomorrow morning at 7AM for the water park, and only people with clean rooms will be getting in the car." This included my bedroom as well because it has to be fair, so my wife and I would straighten up.
Friday at 6PM, my BPD ex-wife would head upstairs to clean the kid's room. I'd object. She'd say that she's only going to help her or supervise (which was always a lie). We'd argue. The kids would argue. I'd argue with the kids. The BPD kid would start throwing stuff in the other kid's room. Chaos ensued.
Friday at midnight, the house is firmly divided. My BPD wife and BPD kid would insist I was being unfair and mean. My other kid and I would say they're being irresponsible and lazy. It sucked, all of it sucked. I hated doing stuff like this because it always ended in a disaster. And eventually, my wife would clean the kid's room and we'd all go on a getaway.
In this situation, no...you don't say it is unfair...you stand your ground. Right is right. Wrong is wrong. So there's not a one-size-fits-all answer here. If it's a teacher or someone else being unfair, then sure...you call it as you see it. But if it's someone being completely fair and your kid can't see it, then you have to try to explain it in a loving, nurturing way.
I was horrible at that because I was always the bad parent, the mean one. But I don't regret any of it because a BPD child needs to know right from wrong. There were a few trips we dropped our kid off with grandma while we went on vacation. I hated it, but it had to be done.
I hope that helps!