I don’t get fussed about it for myself because I know there is a large population on the internet that considers everything fair game and I post accordingly (not that I create so much stuff that everyone wants, haha). I learned that lesson twenty years ago when I spent ages in MS Paint creating a forum avatar for myself and soon started to see it popping up on other people’s profiles. I realized then that something might be legally* mine, but good luck enforcing that. Maybe most people also realize that and post knowing that they will be losing some control, but I don’t think that means we just give up all courtesy.
As far as sharing, I’m all for it - it is absolutely one of the best things about the internet. But to me it means sharing the link - “hey guys go read this cool thing” and then people can go and read and engage with the author on their work. Maybe you include some quotes with the link to give some context for sharing. It’s the wholesale cut+paste for the purpose of building up a different community that the author is not part of that I don’t care for.
Where I draw the line is a good question and I’m doubtless not always consistent. Memes? To me, the sharing and transforming is part of the nature of a meme - images are combined, text is updated or replaced, etc. Comics? Sharing one panel or whatever and directing to the artist’s site seems like the courteous thing to do, but if you are reposting so many of the artist’s comics that people just read your posts instead of going to the artist’s site I would consider that a problem.
Additionally, one benefit of requesting permission from the authors may be to attract some of them over here. I’d love to have more users passionate enough to write 5000 words about some obscure stamp collecting scandal on lemmy.