I'm really mixed about artistic ownership. I think to be either black or white on the issue is a bit harmful to how art flows across the world. I know that sounds cheesy, but that's sort of how we as people change and our ideas move. Once we 'birth' something, be it an idea or product or philosophy, it goes into the world and travels to everyone. Everyone puts their interpretation on it and it changes, sometimes for the good, sometimes not. You cant put the tiny art chick back into the egg. (Unless you trademark the art chick. Then you can shove his little yellow butt wherever you want.)
In the case of art or characters, It's a really hard call to make, morally that is. For example, when I go to cons or look at art sites, I see tons of absolutely incredible art of commercial characters. Art of characters that I have no attachment to, but the creator has put such a beautiful or unique spin on it that I love it. I might love it enough that I want to own it for my wall or just to stare at in awe. If I want to purchase the work, it's probably not because of the character, but the execution of the image. I'm wanting to pay the artist for their craftsmanship or work, not really the character. The artist has made an image of something that I love enough to pay for. It makes me happy to see people take things that exist and make them into something more than they were. Do I think this artist is a cheat or criminal? Not at all. It's very natural for us, as people, to use existing ideas that inspire us.
Now, the flipside of that is when people have no inspiration to change something or make it neater or better. They just sort of copy things and reproduce things. For learning as a kid, we all do this, but we eventually outgrow it. Im not a big supporter of those who do nothing but copy or use existing ideas or characters without change. Its not hard to tell which 'fanarts' were made with soul and which weren't.
Lastly, there's much more minor ownership, like we all here might like to claim on our own work. Im also in a weird area on that aspect. While I would like to think we should all be able to claim our ideas or characters and lock them down indefinitely, that just isnt possible. Someone's going to interpret it or redo it at some point. Would I like that? I dont know. Maybe not, or maybe their redo of my work would be way better, and I would love it.
I dont really see the use of pop culture now and then, or other IP as morally reprehensible. Even ideas that come close to others' ideas, that happens sooooo often, it's impossible to stop it. Putting a stop to it means stifling new interpretations. Some of those new interpretations might refresh an idea or show it in a light you've never imagined. That is pretty cool to see