What is your definition of a vanity press? Mine is that it will publish anything from anybody.

Sure, there's lots of good stuff on there. But there's lots which is not good. Publishing there is not doing science. Science requires peer review.

Its a wonderful resource, but when overworked journalists (or worse, AI) just picks up a paper from there and writes a breathless article on how cool this new idea is, it is misleading to the general public.

Worse, it can get the general public (and from the comments here, even people working in the field) to forget what science is and why arXiv is not a scientific journal.