I too am astonished over some people's vitriol on the subject. I saw someone post over the weekend that said that they'll refuse to use #nobot since it's opt-out, and they'll instead just file GPDR requests against the companies that try to follow them. They demand opt-in.

It was certainly a fiery post, but this is how the web has worked since forever. Whether it's robots.txt or #nobots, opting out is required. After all, you're putting the content out there. In the end, this should be addressed by modern clients: "Do you want your posts to be searchable and your following list to be used for recommendations? Yes, No" and add #nobots if they decline.