Having had my own issues with what can be called Fi, I also have a lot of respect for it.
An artist of recent discovery is Petr Pavlensky, an actionism artist (in contrast to performance art) who makes his idealism known in opposition to Putin's regime in Russia by committing public acts of self harm. He once sat naked on the Red Square with a nail impaled through his scrotum, for example (This work is called Carcass and is to do with 'apathy, political indifference & fatalism of modern Russian society'). Or sewed his own lips shut outside the Kazan Cathedral after the jailing of Pussy Riot.
Essentially the state can't do anything to him he hasn't done to himself already. To me this is at the heart of Fi, that is the sovereignty of self and the selfs of others. I'm not advocating for the Fi - preferenced to self harm themselves, but I thought it was a good illustration of its power and necessity, particularly where those individual rights are most at risk or oppressed.
Those strongly felt notions of violation and injustice tend to be motivators that are often overlooked. But there are negatives as well.
I think when people have issues with Fi in typology, it's when people kick up a fuss over a perception of injustice or personal infringement that can't readily be identified, or which is perspectively minor in comparison to larger issues. The "I have the right to do what i want, when I want but to also be left alone when I want" is fine... right up until it starts to infringe on someone else's right to do what they want. That's where I'd hazard most of the Fe & Ti clashes with Fi come from.
Then we get these situations (I've been a catalyst and directly responsible for some on here.... me getting all roused up over clashing with an Fi member) where it's just a series of stubborn back and forths; the Fi digs in and whines about sovereignty, the Fe looks about for external support that it's ways are best and that Fi isn't considering others & and Ti goes "this is all bullshit, it doesn't make sense, back to LOL."
What's usually missing is a bit of perception on all sides involved. Life can't be always what you want Fi, just because everyone supports it doesn't make it right Fe, we're not entirely rational beings Ti, including yourself.
A simplification, but you get the jist.
*EDIT*
It's probably undervalued because there is currently a lot of substitution for it in day to day society. People who talk about and claim their individuality in a very mainstream and collective way. People with big egos and bigger chips on their shoulders, who latch onto social and political issues in order to plump themselves up.
It looks like Fi, might even be it in some cases, but it's ultimately undermining.