I'm resigned to the fact that fan art will never be my own original design I know I can't sell my fan-works (but perhaps, with some permission, my fandom OCs are plausible for selling, but who wants to buy that? haha)
I respect the original creator's copyright but that won't stop me from doing fan art. So my opinion is fan works should be tolerated, as long as they aren't sold without consent of the original designer. Heck, you might even make more if they commissioned you to make art of their original designs. Licensing and all that
For now, fan works are a ticket to getting attention in the art industry. You use fan works to practice your skills and make works for your portfolio (and I have decided to do that also, haha). I heard that some Avatar:The Last Airbender fan artists now work for Mike and Bryan on Korra I also saw this this anime-ed version of a scene of the Simpsons and the dA user said it helped her get a job.
Why should people make money off of someone's idea? If you though Spiderman was SUPER AWESOME! So you created someone called...Arachnidman, who used the same colors and almost had the exact same story and you thought you were inspired and creative, you're really just a thief, IF you try to make money.
Labor? You wanna know what REAL labor is? it's coming up with an original character or idea. That's what labor is. Fan art is fun every now and then, but devoting yourself to it is unoriginal, and selling it is illegal. Someone else worked hard to design it, why not design your own?