[Careful, I'm an unhealthy ENFP. Biases will occur.]
To introvert your feeling means to look inwards and project what you feel unto your perceptions.
It results in
-A form of constant empathy
-A sense of connectedness
-A sense that if you use your heart alone you can guide yourself through life.
-A sense of right and wrong
-A sense of reading people's intentions and being sensitive to their underlying psychological mechanics.
-A decreased necessity for security.
Picture a kid playing with dolls but that seriously believes she is those dolls.
For conceptual purposes imagine said girl cutting out pictures of her own face and stapling them over the dolls'.
Because she is no longer "herself" and everything about her is transfered unto the dolls, is it any wonder why all of them feel "connected"?
She -is- all of them. Anything that happens to them is immediately transfered to her.
The magical sense of "right and wrong" is an inverted form of ego self-protection.
If you -are- many people, the last thing you want is for one to harm the other because its the equivalent of harming yourself.
Meaning, you will do absolutely everything in your power to stop anyone from harming another.
Say this girl transfers this emotional "doll world" into the real world.
People aren't people, they are all her. The problem is that unlike dolls, people are not under her control.
This is a bit conflictive. People say all sorts of things, they have all sorts of opinions and views.
Because she projected herself, whenever anyone says anything.. its the same as her own opinion being expressed.
This automatic appropriation comes from reflecting herself unto them.
The result is that she must integrate and decode everything, check and check again with the "values" so these new dolls don't hurt each other and in turn hurt her.
The entire value crusade is self-preservation.
How do you stop these seemingly uncontrollable dolls (people) from causing each other harm?
Study them like hell.
Their every move, the tones in their voices, not so much what they are saying but anticipating how people's particular views might have future repercussions for conflict.
If people are racists, homophobes, misogynists...they are wrong not so much because the girl in question intellectually debated all these issues.. but because they feel wrong, they feel nasty... they might cause future indirect self-harm.
When it comes to the selfishness issue between Fe and Fi, neither is more selfish or more manipulative. The complexity of manipulation depends on the strategic intellect of the individual to defend her ego. If ego is centered on the self (Fe), that person will do everything to defend themselves... lying, cheating.. whatever it takes to protect their emotions in a completely natural fashion. If its not centered on the self (Fi), that person will do everything to defend the world but not out of virtue or technical philosophical value.
To use your heart to guide yourself through life is a romantic way of seeing things, more common to NFs in general (seeing as we prioritize feeling). Fe's will go through life actively protecting themselves, studying hard, looking at possible advantages and downfalls of every action for themselves. Fi's will probably appear to be lazier and less directly ambitious because the self is not in them but in others, as long as others are in acceptable degrees of harmony (in which they rarely operate), the Fi's will feel safe and not necessarily compelled to work or study hard (calculation comes in whenever not studying or not meeting the deadline might cause future harm).
It is completely natural for an Fi user to develop resentment toward society and Fe users. "They" are always causing trouble. Society insists there are differences, financial, racial, sexual, cultural.. to an Fi, these are all "dumb rules" and people should just simply treat each other nicely. The more clever the Fi, the quicker she can come up with excuses to reduce these rules. Big fans of cultural relativism unless they decided to pick up some random cause the minimizes hurt in their immediate social network and think that by sticking to it they are being virtuous. Anything that casts doubt on the system validates their construct.
It's not difficult to imagine that they have a very big interest in manipulating people while simultaneously playing the good guy. Manipulate people to make them happy so their happiness is reflected back at the Fi user. Manipulate people so they don't hurt each other and cause harm to the Fi user.
Why I think Fi is... a sad human condition is because Fi users will spend their whole lives chasing and pleasing specters of themselves in others. It's a bit depressing that a person should be stuck in a glass cage their whole lives. Never really seeing people's faces, never really experiencing life but decoding the whole world into good/bad. In some sense, all the connections in an Fi user's life are completely fictitious. Fi love for example, is really a sick form of narcissism, not a genuine connection between two people. No real parent/child relationships, no real friends, .. the world of an Fi is a world of dolls whose information must be immediately transduced.. that and nothing more.
Based on these observations, I propose that Fe shouldn't be dismissed as just "the social graces" or merely waving loyalty flags. There is something healthy, brave, genuine, frail and human in Fe. That is, existing in one's own body and assuming one's own feelings.
Tangent= Is it too much of a leap to think that much of spirituality can be explained in this fashion? People who sense auras, places, signs or spirits (the majority of spirits, are conveniently divided into good or bad spirits) are probability Fi users projecting their feelings into the inanimate (But that's another conversation.).