Is fan art Plagiarism??

Here's my task for you, my fellow otakus of the world:
Consider what forms fan art takes (i.e. drawings, sculptures, doujins, cosplay, fan fictions, ect ect.)
Should someone be able to make a profit from selling art in which the subject isn't their own?
Is fan art a learning tool for improving one's own style or just plain copying?
Take into consideration all this and anything else you can think of and give me your well informed opinion.
I need it! Really, I do. (for school)

Answer it and pass on this annoying conundrum to your fellow otaku and force them to answer. You would be surprised how contradicting truths to this can be! You will be contradicting yourself!

Note me or post your response here or even in a Deviation of your own! I crave your response and also kind of need it to do my study.
(and in a timely manner please!)
If I like what you say or draw, I will some how work it into my final project and you will be loved by many students here. (Yes I will credit you and no, you don't get paid but by kindness)

Thank you for your help!!