Earlier quoted context omitted.
Scraping is legal, but IIRC scraping authenticated contents is not. Isn't Nitter abusing account sign-in for this?
Anyone can make an account, though, and instantly access that content, so Elon doesn't really have any leg to stand on by claiming they're private. It's not the same as Cambridge Analytica scraping stuff you had to have certain privileges to see by tricking the system into granting those privileges.
It's like a club that checks ids to ban people. I wouldn't call that club open to the general public.