If Fi was as generous and kind as some descriptions make it out to be, then there would never be a use for any morals, religion, philosophy, interpersonal instruction, or ethical discussion under any conditions - for the fact that some people are merely born/naturally inclined to be one way or another. In this neat little world, no one can be commended or blamed for anything. It's all type related.
I'm being a little extreme, but my point is simply to point out the uselessness of subscribing too much to functions.. especially labels like "nice" and "mean". Life is more complex than this. Typology is a neat way to try to break it down somewhat, but at the end of the day, it's only a small piece of the puzzle. You won't find all the answers here. Or who knows.. maybe it's worse. Maybe it's complete bullshit. =)
Besides, it's good to give the rest of your life/experiences some credit anyways. I mean, if you ARE a nice person.. and a Fi type.. don't just say it's Fi. You got to that point in a much more rich way, I'm sure.