Yes people are layered, but there are some who are genuinely good or cruel. There are habitual trends and intentions that help to define us.
^straight to the point, so i'll put the cards on the table:
first of all - i can personally vouch that you were quite kind towards me, and have given me some of the best & most thoughtful advice regarding my son that anyone has. which is why i feel rather bad for the potential hurtful consequences this might have - not necessarily in the long run but there's a good chance - which is why i would have rather done it in PMs (edit: actually feeling sort of crappy about it), but given that you've provided yourself here as an example...
i also know that when you brought up the topic of frustration in a discussion, and i told you that something you did after was in fact frustrating and explained why, you reacted by calling me delusional, and (perhaps seen it as a contrast point?) proudly declared that the people who know you think you are the kindest person in the world.
now overall, there's no question that the first balances out the later - over shadowing it completely a billion times over, the later is so incredibly mediocre as far as offenses go, frustration in an online discussion is something that people cause each other all the time - i wouldn't be surprised if i am doing it to you at this very moment (it's not my intention but it is a possibility) - people make each other frustrated on the road and on the street on a rather consistent basis. it's incredibly... mundane, casual, barely worthy of bringing it up in the first place - i wouldn't have in that discussion if you wouldn't have pointed me towards it in the context there. i would wager that by most ethical systems killing a fly is probably worst.
undoubtedly, going by nothing but those two interaction, i would certainly say you've being rather kind to me. for god's sake - aren't you a social worker or something similar? i got the general impression that your job (or past job?) consists of helping people, probably for for shitty pay. chances are, you have been quite giving and helpful many times in your life. overall i have a positive opinion about you, for whatever that might be worth. chances are - and admittedly i have very little to base that on - you are generally a good person.
but, while there are many things i am not particularly an expert about - the inner working of hummingbirds for instance - i am the outmost expert regarding my own experience, of... anything. i in fact know when something frustrates me because - and yes a T is about to use the F word - i feel frustrated by it. it's also not something i hold much weight on or consider a big deal. but it's absolutely irrational to think someone is delusional in reaction to their own experience - it's a real event in a real skull which belongs to a real human. so the question remains, why would you feel the need to declare me delusional in reaction to my description of my own experience?
my theory is that it's the same thing you've done here: just like you see a case where you are fair as a contrast to the possibility there are cases you aren't, so did you see the case where you did something you would consider unkind as a contrast to all the times you were. if the nature of my experience at a given moment provides a contrast point, i am taking away your entire ideal away from you, so telling yourself i was delusional regarding my experience was your way of coping with it. in essence, you think in absolutes, so you need to believe the things about you in terms of absolutes. it's not "i am mostly a kind person", it's not "i try my best", it's "the people who know me think i am the kindest person they've known". there's no leeway, no room for errors, so any hint of an error must be wrong. this is useful for painting a rather beautiful picture, a clear cut character which wouldn't be wrong in a piece of fiction, but it gives no room for genuine accountability. it's this very sort of thinking it's direct consequences that provide the common pattern for most of the negative feedback regarding INFJs - it explains most if not all of of the behaviors.
take these 3 traits:
1. determining value by the value to others.
2. judging conclusively within absolute terms.
3. being able to reject facts that don't feel right.
introduce low self esteem into the mix - the lack of seen inherent value in yourself - and you end up with the perfect recipe for needing to paint one's self with absolute ideals regarding one's self of one's own value to others, both the ability and the need to discredit and/or discard anything that might imply otherwise... and you have the negative stereotype of INFJ emerging from it.