I actually liked Kes. I'd have preferred her not to have been written out at all but if the writers are never going to use the character again then what's the harm in giving her this storyline? I agree the resolution was lame but at least she didn't go through with her plans in the end. I don't think Kes or the events of this episode were ever referenced again so it's easy to just pretend it never happened since it had no long term impact on the series.
If you look at it rationally ('it's only a show, we can do what we want as long as we are making good stories and entertaining the viewers'), that's true. But if you're going to 'dump' a character that has been on the main cast for several years, gathered a fanbase, and not giving him or her an at least somewhat nice sendoff, that fan group is going to be annoyed (and I'm just talking about moderate fans here). There's a difference between doing it to such a character and to the one-time-alien we never saw before this episode.
Suppose Tuvok had been revealed to be a Romulan spy in Endgame and met his demise just minutes before VOY reached the alpha quadrant. I suppose the Tuvok fans wouldn't have liked it. Even though in all likelihood, writers were never going to use the character again.
People didn't like the "unneccesary death" of Kirk. The ENT fans didn't like the casual death of Trip- and neither of them went on a rampage and tried to kill their former friends. I suppose people like to see their "hero" end on a positive note.
There is one scene I do like in Fury though, which is the goodbye scene between Kes and Neelix in the transporter room.
I see your point but again I have to say that not all characters end on a positive note. Tasha Yar and Jadzia Dax died senseless deaths. At least Kirk got to die saving a planet. Yar was killed by a giant pool of shit and Jadzia was murdered for being in the wrong place at the wrong time.
I think the issue with Kes is that she was no longer a main cast member and the writers had already made it clear they had little interest in her by writing her out in Season 4. I'm not sure if the fan campaign was the reason behind her return or not but they no longer appeared to consider Kes an important character and didn't show any deference to her in Fury. They still cared about the main cast and Kes was no longer part of that so was fair game for whatever they came up with. I can see why it would annoy her fans though.
I also liked that last scene where she asks Neelix if he sees anyhing he recognises and he replies "just you". To me that was a bittersweet way to end her character and I liked it.