I don't think that's true, most cases of doxxing happen with publicly available information. But I guess you could argue doxxing isn't really "illegal."
Most doxing involves using publicly available information to harass others... and yet that behavior is frowned upon everywhere. I don't think anyone here honestly believes that account was used for anything other than to encourage the stalking and harassment of Elon Musk because the account owner simply doesn't like him. I also don't think anyone here seriously believes that stalking and harassing people is "free speech". I do believe people here are letting their class bias show.
How does flight data encourage stalking and harassment? The account is run by the same person who tracks the flights of other wealthy and notable people as well. Why weren’t those taken down?