They're nothing new. They're as old as fanzines-- meaning they predate the internet when it comes to fandom. I've been active in some form of online fandom for 7 years, though really only active in community/forum stuff for about 4 or 5 years, and they've always happened. But LJ has made a lot of stuff almost post-modern self-conscious in a way, so it's not considered polite to flat out argue about ships in general communities, just in ship-centric communities. Ship--centric communities can and do bash other ships, though. What amuses me about Avatar fandom is how strongly people react to the slightest amount of anti-ship stuff; they're hyper-sensitive to ship wars before they happen, so the only thing you ever see is vague squabbling. Shipper bashing is just rude (that's knocking the speaker instead of the opinion they voice), but I see nothing wrong with knocking the pairing itself, in the appropriate forum.

For example, when that person posted the anti-Zutara fanart earlier today on avatar_fans, I disagreed with the idea that what they were doing was satire, because it wasn't. I didn't really care about the fact that they were knocking my ship (it's so hard to care about the little stuff when 3/4 of the fic that appears is my ship), but I was annoyed that they thought what they were doing was "satire" and not just plain bashing. As a fan of satire I was offended, not a fan of Zuko/Katara. But that post would have been perfectly acceptable at a katara/aang community or the_shipper_state