FWIW, I think describing these as "non mainstream" and the entire description of these communities sounds to me ... somewhere between biased and pejorative. Makes it hard for me to keep engaging in the discussion.

For the record, while the rationale can be flippantly described as "I don't like clicking things", I'd like to give it a serious description.

Another idea of how to structure this would be to have the email when new receipients are added contain some boiler plate at the bottom: