These researchers are making public scraping that was already happening in private. Do you really think they were the first ones to realize that public Discord servers were public?

On the contrary, kudos to these researchers for bursting the illusion that people previously had that things said on public servers somehow would be ephemeral. That's not how the internet works, that's not how it's ever worked. If you send something to someone else's computer you have always had to assume that every recipient could have made a copy of it, and when the recipient list is "everyone who ever joins a public Discord server from now until the end of time" that makes it public information.

Better that it be widely recognized and talked about as these researchers are doing than have accessing public data remain a dark art that lay people mistakenly believe can't happen.