It was meant in jest, I should have contrasted plain text / cipher text to be more clear. Though it’s a similar kind of extenstion to email technology that they are advocating against.

These folks want to read their emails in their terminal email client, and for you to cater to their limitations. If you use tuta and send them an email, tuta just emails them a link to view the message on tuta’s webapp. I’d say this anti-HTML group aren’t fans of that.

Not to argue semantics, but I would consider encryption in general is a change in message formatting. The client needs to change how the bytes are interpreted. It adds complexity, and clients may not support it, their exact arguments against HTML.