Like, by quoting me on HN you're actually violating the content license and terms of use agreement (you're only allowed to use your "user content" not mine). You'd argue fair use, and you'd probably win. But nevertheless you'd have to argue it.
I think we're in the weeds with copyright. What's the problem we're trying to solve? A federated public communication protocol/system. What do centralized platforms do in the face of copyright? Require users essentially forfeit their copyright over the content they post (if they're nice limited to the scope of the content traversing their network). Why? Because it doesn't work any other way. What is the expectation I have when reading a public post? I expect I am allowed to read it, quote it, remix it, etc. because it's been posted publicly. Nobody asks permission to quote each other even though they technically should in accordance with US copyright law. How would a discussion transpire without a shared understanding of how the content is allowed to be used on any network?
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And I mean if you really want to get into the weeds, copyright prevents you from e.g. playing a digital music file on your computer since the bytes need to be copied over the network, into memory, onto output devices, etc. This was the original observation: copyright basically prevents you from doing anything digital with any digital media. That's why everyone needs a license and we're in license hell. In digital it's copying all the way down so hit it with the copyright hammer.
Imagine if we applied our digital understanding of copyright to traditional artwork. I have a painting. You visit. By shining light on the painting I'm reproducing the image on your retinas. You say copyright violation? I say preposterous! What if I take a picture of the painting that I own and show you? Uh oh.
Copyright just doesn't make sense when applied to a public social network. At all. And it doesn't make any sense because a social network isn't about artists trying to make money off their works, it's about anons trying to win internet points for the day.