Well, parody, while derivative, certainly is not subject to the control of the original author (remember the Luke Skyywalker case).

I think the courts should have a very liberal definition of what is transformative -- the permissions culture has gone way way too far (this infects both civil and criminal law in the USA and Europe).

Sure, parody is fair-use as per Justice Story, but that's where this all gets gray. You can claim fair-use, but unless it's quite obviously a parody or educational, etc., you're going to have a tough time if someone has a mind to sue.

What about works that are inspired or influenced by other works? Nearly all works are. In some homeopathic sense they might be derivative. I assume there's a grey area between that and clearly derivative works.