I have no objections to reading or writing fanfics.
I have read some brilliant fanfics (Myr's HP stuff is amazing) and I have read some truly awful pap (including some Malcolm in the Middle stuff that I really wish I could forget).
I think to a large extent most of what is written today could be viewed as fanfic in some way or another.
For example, many of the Star Trek novels are not written by any of the original scriptwriters. Modern remakes of films rarely involve any of the original scriptwriters or the people who came up with the concept. Many TV shows are based on old films and vice versa. These are all established universes that exist that a fan has simply picked up and ran with.
The only difference between them and us is that their works have gained mainstream legitimacy in one way or another.
I have to agree with earlier comments that there is probably very little in the way of modern literature or TV/film that could be called truly original. If you look hard enough, you'd find something that has already been used at least a dozen times before.
I have been known to write the occasional fanfic and slashfic (mostly slash). Sometimes they are true to the established universe, sometimes I see just how far I can pervert cannon.
We already know from several sources (including JK herself) that she had planned a huge HP universe, and a lot of in minute detail, that we never got to see - most of us thought that Blaize Zabini was a girl for the first five books. Her list of all first year students included who were purebloods/halfbloods/muggleborn, who were in what house, and even what their ethnic and geographic origins were. That is a lot of pseudo-cannon for fanficers (is that a word??) to use.