I see this as a temporary problem however because LLMs are transitional. At some point it won't be necessary to train an LLM on the entirety of Reddit plus everything else ever written because there are obvious limits to statistical models like this and, as a counter point, that's not how humans learn. You may have read hundres of books in your life, maybe even thousands. You haven't read a million. You don't need to.
I find it interesting that this issue (which is theft, to be clear) is being framed as theft from the site or company that "owns" that data, rather than theft from the users who created it. All these user-generated content ("UGC") sites are doomed to eventually fail because their motivations diverge from their users and the endless quest to increase profits inevitably drives users away.
Another issue is how much IP consumption constitutes theft? If an LLM watches every movie ever made, that's probably theft. But how many is too many? Like Apocalypse Now was loosely based on or at least inspired by Heart of Darkness (the novel). Yet you can't accuse a human of "theft" by reading Heart of Darkness.
All art is derivative, as they say.