Well... I wouldn't say Fe is big on my list of most used functions, though Ne can often compensate for lack of it and also be confused for it.
Much of my reputation has come from certain people giving me lots of points at a time "because I like you" or because they seem to want to include me in a social circle of sorts, and so if they see me falling behind, they look up my posts and just click, click, click the rep thing. Having said that, I've also earned a lot of points through people reading and appreciating my actual post contents. But you could equally say that the people who just "like me" do so because of my post content, generally, so either way it's earned.
As to whether Fe is positive or negative on this board or anywhere else on the Internet, I'd have to go with positive, but no more or less so than any other function. Simply because I believe in diversity being a strength, a good thing, without which things tend to degenerate into mob-think and before you know it we're wearing white hoods and burning crosses... um, sorta.
So I'd always rather include something, than exclude it, in general.
However, thinking about the nature of Fe and what it does, it's a very powerful function in that it can ascertain a person's emotions, perhaps even when that person isn't even aware of them themselves, and then respond to/manipulate them in ways which leave little room for manoeuvre. This could result, if it's used badly, in alienating people with strong value/personal attacks, frightening them off from saying anything.
This brings to mind for me female style school bullying. The main difference between female and male bullying is that male bullying tends to be Te driven, whilst female bullying is Fe driven. Whilst the boys will generally leave you alone after they've let you know in a very obvious (physical) way that they don't like you, the girls will never, ever leave you alone, and will not rest until they've verbally pummelled every last bit of self-esteem out of you, to make you think of yourself as a pathetic loser, a person nobody could possibly like, and to ensure that nobody else likes you either.
This might also be a side effect of the boys' bullying, but it's not intended and often if the boys are made aware of the damage they've done to the victim, they feel guilty about it and often apologize and want to make amends. But I think that with the girl bullying it is intended, and if the subject is raised, they believe themselves to be fully justified in what they've done. (this comes from my experience and may not be universal)
In my experience, the female bullies were known as the popular ones in the school or workplace. That is, they thought of themselves as popular. But it wasn't true popularity; in reality, people were just terrified of them, and of being their next target, and so generally didn't express openly their true opinions of them. And if anybody did, the bullies' Fe could easily spin it to look like that person was just bitter or mean or stupid or whatever, so that nobody would take them seriously and nobody would openly back them up, even if privately they wanted to.
Obviously this can translate into internet forum culture as well... so... whilst I'd say that a healthy and positive manifestation of any function, including Fe, is very welcome and a positive contribution to anything, there are always the possibilities of not so positive uses of it coming in.
I wouldn't say that mature, adult ExFJ's though are the main culprits for this. In the main, their use of Fe, as it's their dominant function, tends to be more positive, as they're more aware. Well, here anyway. I think that in adulthood, the danger of Fe abuse comes more from those of us who have it as a tertiary, shadow or inferior function, where we're not always aware we're using it, and when using it, often don't use it correctly.
The footprints of inferior Fe at its worst can be seen all over INTPc, where very negative and oppressive vibes can often run rampant all over the forums, where everyone's in the grips of it but nobody's aware of it and they're all denying it. They're being mean spirited and rude and self-righteous but all the time convinced that it's pure logic and reason that they're acting under. Of course it's not always like that, but situations like that often do spring up, which I think illustrate the negative impact that bad Fe can have.
I think though, that an ExFJ forum wouldn't be that way. I've never visited one, but I can imagine what it'd be like from thinking about my relatives at a family gathering - most of my aunts and sisters (and I have many) are ExFJ and when they get together it's usually very warm and pleasant and welcoming. That's the difference to me, of good Fe and bad Fe.