What is your opinion of fanfiction? Do you see it as theft of intellectual property or copyright infringement or is it simply a flattering way of saying “I really love your work”

Technically speaking, fanfiction is an infringement of copyright, and if someone gets paid for that, without the permission of the author, that’s definitely a violation of copyright.  At the same time, I don’t have a problem with fanfiction that’s restricted to a comparatively limited number of fans and not used in any commercial fashion. Fanfiction in that sense is a gesture of appreciation, but I would hope that it might be the first step for many of those fan writers toward creating their own worlds and characters, because we can always use more good writers.