It’s about time that people understood that “Everything on the internet lasts forever” is a falsehood formed from a Web 2.0 mindset. Now those big Web 2.0 sites everyone thought would dominate the internet forever are dying, and the only thing saving what was on those websites (the internet archive) is being constantly sued by greedy publishers.
I think that warning is more about the lack of control you have over your own data. You post a pic or political view online and it will be duplicated before you know it and you won’t be able to delete it on your own terms.