Oh yes. Several times I've gotten into an argument with an anti-fanfic person who's taking the "it's my creation and it's perfect and how dare you sully it by putting your dirty derivative works all over it!" moral/ethical stance, and I'll ask them if they have the same moral/ethical issue with people singing Beatles songs as they walk down the street... and every single time they've said yes, that is also unethical and a violation of creator's rights.

Also there was that that case in Scotland where someone got threatened with a lawsuit for unauthorized performance for singing while she stocked shelves.