My values are generated within and often go against those of people around me; my thinking also relies more on inward processes, so often I end up going against the mainstream.
However, I don't think that the passions of Fi are fleeting. Logic changes my values, but the feelings that produced those values stay the same. And some values are buried too deep for Ti to work away at them - the belief that all human beings are more important than any system they live within, for example. Those values might be logically disproved, but the feeling behind them is strong and constant and so they don't change. But it's hard to pinpoint exactly where Fi values come from - what cognitive processes bring them to being, where the solid foundation lies - and so I can see why it would seem that they might be more fleeting, changing throughout a person's life.
EDIT: Just saw this:
"In recap firm establishment of values requires a solid foundation of beliefs, the nature of Fi does not provide that."
I'd disagree here and say that the feeling functions provide a more unchanging foundation than either the thinking or the sensing ones, which are constantly processing new information. Not sure about intuition. Yes, I know that feelings seem to change from day to day, but at least for me there are some strong feelings that I've had since I can remember, and those never change. Compassion, for instance - that's one I've always had. It never leaves me and it drives a good portion of my actions, often flying in the face of logic. I suppose it's possible that something drastic might alter this and thus shake my foundation, but I don't find that too likely.
Guess you could put feelings into at least two categories - moods and passions. The latter are pretty unshakeable.