"I steal from every single movie ever made. If people don't like that, then tough tills, don't go and see it, all right? I steal from everything. Great artists steal, they don't do homages."

This is why I don't have a problem with fanfiction. It's just the impulse of the writer to emulate worlds and ideas and characters that they love. And other artists do this constantly.

It actually doesn't remind me of anything so much as it does a cat playing with a bug. Kittens will do this for practice, and cats will do it for fun, but at the end of the day it is taking a piece of some other artist's work and riffing on it for entertainment and/or training purposes. Some writers see it as a crutch, but I see it as a way to isolate different aspects of writing stories you need to practice while being able to handwave the parts you're not trying to focus on. So if you're trying to improve your characterization, it makes it easier to focus on that aspect if you just use an established universe and throw an original character into it. Or if you're working on setting, you can take characters you already know thoroughly and put them in new places.

I'm of the firm belief that once you put a piece of art out into the world it's up for grabs and/or interpretation and you don't really own all of it anymore. That goes for fictional characters or dance moves or photographic techniques or anything else.

Artists will always steal from each other. Everyone just passes the art around and puts their own imprint on it.

We've been telling the same stories for hundreds of years, essentially. Read Joseph Campbell's The Power of Myth if you really want to go down the rabbit hole.