MY THOUGHTS ON FANART ICONS.
I feel that it is rather douchey to take art that you know full well the artists would prefer not be iconed/otherwise modified and icon it/otherwise modify it. You can come up with all kinds of rationalizations and justifications for it (it's no different than using official art! It's just icons! They're making unrealistic demands! AND SO ON) but in the end there's really no getting around what it comes down to...
Which is more important, your need to use that icon or the artist's desire that their work not be used in that way?
It kind of bugs the fuck out of me sometimes that so many people in fandom get so intensely defensive about their belief that their need to use that icon trumps the artist's desires. That's what I'm talking about when I complain about "entitlement complexes" in regards to icons in fandom.
At this point a lot of people will bring up the fact that the creators of official art might not like it if you icon their art, either, so what's the difference between that and fanart? I have three main lines of thinking on this:
1) It's easier to find credit for official artists. Look them up on IMDB or AnimeNewsNetwork, or find the full version of the iconed image that has the artist's name in the corner.
2) Official artists get paid for their work. They've already received compensation for it. Fanartists share their work for free, and all they get in return is recognition. Grabbing their art and making uncredited icons for it is rude.
3) Fandom is a community, even across language borders. As a fellow fan, it's only courteous to respect the artists' simple wishes in regards to their own work. You can make noises about how they should loosen up all you want, but in the end that comes down to the entitlement complex again. It's kind of rude to decide that your personal feelings about the use of fanart trump the feelings of the person who made that fanart and shared it with other fans in the first place.
After all other arguments have been exhausted (or sometimes before), people will say, "It's just icons! It's no big deal. It doesn't really matter!" To which I say: yeah, I'm not exploding in white-hot rage or anything. But being douchey over a small thing is still being douchey, and it still bugs me.
As a side note: somewhere along the line I started classifying fanart use in icons into a Scale Of Douchitude. "This version of my character barely has any official art, and I try to credit the artists in comments" is on the acceptable end of the scale, "I really like this image and wanted to use it sometimes in my personal LJ" is in the largely inoffensive middle, and "Why shouldn't I make and share icons of every image I pull off 4chan? They're pretty, and I refuse to limit myself!" breaks the Scale Of Icon Douchery for me.
tl;dr summarized: the use of fanart icons boils down to a simple decision. "Which matters more: using this icon or being polite to the fan who made the image?" Most of the time, I think people who decide that using the icon matters more are being rude. It wouldn't bother me so much if they weren't so aggressive about defending their choice.
And no, just to be clear, I don't really care if you use some fanart icons on your personal LJ (although I mostly avoid it myself). What gets my hackles up is a) the people who make them in huge batches, especially when they just grab the images off 4chan and then demand credit for the resulting icons (although I could make a whole new rant about that practice), and b) the people who use tons of fanart icons for RP accounts when there's plenty of appropriate official material available.
Obligatory disclaimer about how I am a hypocrite and repost Japanese fanart all the time goes here. But I will point out that I usually only do it under friendslock.