I highly doubt these people were... Mature examples. Mature Fe dominants have been great, but I've only been acquaintances to them.
As for what turned me off of these people? I'll give examples of the two I know.
Number one- Well first off they showed that they cared... and it seemed like a lot at first. They listened to me, took me for who I was, etc. We could relate intuitively. Then I realized that they did that with everyone (like 30+ people that they talked to), and I didn't really feel that special. I had kept talking to them and such, and something just didn't really seem right to me. Like they were acting that way to just be nice, and it didn't really seem like the person cared. It was odd, there was no real conflict (most people I make friends with we disagree on something and get through it, and learn from that). It was like she was just... agreeing with me. It felt very fake. I did an experiment and stopped talking to her to see if she would talk to me, and sure enough, she didn't. I had had experiences before with Fe, and they weren't that great. I figured I'd give this person a chance, and I did, and they failed.
Number two- She was just insane. She would cause emotional drama, would think that she knew who you really were (and failed miserably). When she thought she would know how someone really was she would gossip about them. This would cause emotional drama, and she would thrive on that and the negative attention she would give people. She also knew how to manipulate people's moods, and got frustrated with me since I resisted. She then tried to spread rumors, but I stood up for myself and basically said "F*ck you, prove that this happened". Then she basically doorslammed me.
Both of these people were hyper emotional, they didn't seem to care about what my point was in a conversation if it sounded offensive (I'm sarcastic and blunt when comfortable with someone). If it was too blunt and I was too honest they would take offense to what I said, so I had to delicately word what I was saying and pad the truth so I could actually communicate. They would also randomly dump all of their superficial emotional stuff on me... and wouldn't really help me with my problems in return.
They were unhealthy definitely. But as a whole Fe just seems kinda... Superficial to me. That's just the feeling I get. I've met a few older healthy ESFJs, and they didn't seem superficial to me at all. It's all subjective, and I've yet to be subjected IRL to an ENFJ that I can tolerate.
EDIT: Forgot to mention that overly emotional and overly sensitive people in general are just... a turnoff. People who's emotions are very unstable.