Finally getting back to all you folks... TBH, I was intimidated by the length, depth, and quantity of the replies. So, apologies for the delay!
In a perfect world, I wouldn't be a petty, selfish prick and doing the right/kind thing would always make me feel good. IOW, I want so much to think of myself as a good person, etc that accepting that I feel so strongly about such a small thing is pretty mortifying. I tend to keep hoping it will go away and feel ashamed when it does not. It'd be like admitting you're physically attracted to Donald Trump. Of course you don't want anyone to know that about you.
I was almost mortified when I read this post. I thought INFJs were usually great at interpreting their feelings as valid and as signs of things that need to change? My reaction is probably just Fi vs. Fe -- I can't imagine having such a detached and unforgiving attitude towards your own preferences. (Well maybe I can, but not in the same way.)
As for your second question, about "in a perfect world no one would ever know your feelings on the subject", um, have you seen my blog?

In my perfect world, I would immediately know my own feelings on the subject, and I would be sure to convey them in a responsible and respectful manner. There might be a lot of compromise, but very little sacrifice.

Well to be fair, even on your blog, you are extremely even-handed, in a way that recalls the friend I was asking about. That is, even-handed in a way that sometimes makes me wonder whether that's your true opinion on a particular subject. So I should have been more specific, and said "your feelings on the potentially controversial interpersonal subject", or something along those lines.
That makes sense, though. So a lot of it has to do with processing time? (Ni, I guess?)
When I'm around other people I start to internalize their feelings and perspectives as well as mine and view all of it almost like a disembodied entity. I'm not grounded in my own psyche or ego the way most other people are. In this way I'm not making some great sacrifice for the "Greater Good", but it even seems irrational to me to over-value my own feelings or perspectives when I'm just another person like everyone else. I've taken it too far in my own life though as a result of being around people with greater needs and stronger feelings and ideas than myself. At this point I actually go blank when in a group and asked what I desire, and I just give over to consensus. If it isn't something I can tolerate then sometimes I'll end up quietly leaving.
Is it wrong that I sometimes see this as unfair? The INFJs I know will often do this as well, and it sometimes comes across as denying everyone else the right to work with you and ensure that you're happy/included.
Is there a way to work with INFJs in these situations, and work your way into their (usually internal) decision-making process, without pissing them off or making them feel bad?
I have a very deep desire to connect with a few people and be seen and understood. It is extremely difficult for me to venture out to describe a feeling on a subject because I fear it won't be understood. I end up having strong feelings of longing towards people I think might understand me, and a nurturing, but personally distanced feeling to other people (of course there are degrees of both). Being heard might mean almost everything to me, but because I spend so much time observing and analyzing the ideas and assumptions of other people, I almost never expect to be heard even if I speak. I find it conserves energy immensely to not often share my preferences and feelings, but it would be ideal to be able to do this.
That makes sense. I think I have INTJ friends and acquaintances with the same issue. (Ni problems...) I suppose it's just a matter of surrounding yourself with folks who speak the same language -- obviously much easier said than done.
I do let my feelings be known, but I feel I have little concept of how to appropriately do this when there is a strong disagreement between what I want and what is popular and appropriate. If it's just a small preference I can just bring up a different idea to people or do my own thing separate from the group and it'll be fine. But if I am afraid I'll actually cause an uproar I get all resentful and just say how I feel anyway and feel like I'm being immature; either that or I wait until later and ask someone else what they think I should do (like your friend did). I dunno. I usually end up being afraid out of proportion to the situation, and people still like me even if I think I'm being immature. This is part of what I call social paranoia- part being afraid people are going to stop liking me, and part projecting group judgment onto other people. Discovering that this is out of proportion to reality has helped me be more (properly) assertive over the years and comfortable in relationships.
This makes sense. I have INFJ friends who have said similar things to me and I've replied with "I literally cannot imagine a situation in which anything you said would be that controversial. You are far too diplomatic for that." And of course, they act like they have this evidence that I don't have, and that yes, people really DO get that angry with them when they express their feelings. Then again, like I said earlier in the thread, there's no way for me to know how much they're exaggerating.
Sorry I took so long to get back to this.
The terms "harmony" and "Greater Good" bother me. They imply a nobleness of purpose, or a selflessness that I, personally, don't always feel. It's nice to rationalize it that way, but it's not always true.
I would rather say that I tend to adjust myself, or defer, in order that things run more smoothly in relationships (with relationships being between myself and one or more people). I suspect that how I define smoothly may differ from how other INFJs define it, due to different early experiences. I really don't mind conflict as a means to resolving a problem, but I do mind ongoing, unresolved, contentious conflict because that describes my parents' marriage, and I've seen the consequences of that firsthand. That's why I'm a big advocate for honestly talking things out and reaching some sort of resolution, if possible.
I've had a difficult time finding a way to answer this briefly for you. It's just not a cut and dried "this is essentially why I do that" type of situation for me. The whys behind the behavior are varied. If you're looking for a more depersonalized answer, I can only offer speculation. Perhaps I'm more sensitive to certain signals that are present in interpersonal relationships. Perhaps I've learned to interpret those signals based on the very early relationships formed in my family and community when I was, essentially, a powerless child. Perhaps I then identify with being powerless unless I learn otherwise. Keep in mind that other people aren't as sensitive to the same signals, so perhaps I've also learned that trying to explain what I perceive is difficult. So, I end up creating my own interpretations and projections of behavior based on all of that--an Ni model that can be difficult to adjust once it's in place.
So, perhaps I sacrifice my feelings because I feel powerless to do otherwise in order to keep the relationship running smoothly. Which is actually a bad Ni-model to use in personal, one-on-one relationships, because then I'm sacrificing instead of compromising and I will eventually resent that and the person I feel made me sacrifice, when in actuality, I'm the person making myself sacrifice. That's why I had to learn to take responsibility, to be accountable, for my own choices. That way I no longer feel powerless and I don't feel the need to blame other people for my own choices.
Firstly:
Secondly: I would have described the bolded as harmony-seeking/harmony-focused behavior, but then again, my definition of harmony doesn't involve nobleness of purpose, so you were right about differing definitions.
Thirdly (woo, lists): Your last paragraph actually reminded me of an interaction that I had with my INFJ mom the other day, when she asked me, essentially, whether I thought it was valid for her to get angry with people for not asking her how particular projects are going. My response (with a teasing nod/wink/laugh -- and also a comforting hug, later) was: "Generally I don't think it's a great idea to expect someone to do something, not tell them you're expecting it, and then get mad at them for not meeting the expectations that they had no idea you had." Then, of course, we talked about what project she was talking about, and I validated her and (metaphorically) patted her on the knee, and made a note to myself to ask her about those particular projects from now on. Nothing I can do about the other folks she was talking about, except hope that my expectations comment was reassuring/constructive, somehow.
I suppose I also have the same follow-up question for you, as for fia: Is there a way for friends/family to help out with that tendency? To butt into your internal process without threatening your sovereignty (can't think of a non-international-relations-major way to say that

)?