I don't really see anything wrong with fanfiction.
It mainly stems from just being extremely creative and/or having an overactive imagination, which is not really a bad thing.
I don't write it, which is weird because I LOVE to write and it was the one thing I excelled at when I was in school. I dabbled in writing fanfiction a few years ago but would probably be absolutely horrified by my writing/grammar back then if I ever looked back on what I wrote.
Anyway, the writers/readers know that the things they write/read are, in fact, fiction and have never and will never happen. In my opinion, it's like reading a fictional book (just with well-known characters) and as dumb as it may sound, it's like an escape for some people to "live" in a fantasy world for a few minutes.
I'm sure there are at least a few people in the world who are confused between what's reality and what's not, but that's a whole other thing.... 0____0
So no, people who read or write fanfiction are not crazy, thank you. Just very creative and have big imaginations. What are you doing with your time aside from trying to insult people on the internet? Lay off, yeah?