This sounds great until you realize that, in the real world, people want to have some options to format the text they write (italics, bold, hyperlinks and the like), and there's absolutely nothing wrong with that.
Then they top post their entire email to a 257 email chain, so you have to do a kind of inverted scavenger hunt in order to figure out what they're talking about, none of which is improved or aided by the company logo, special font, or image links to nine different social media accounts.
And I haven't even gotten to grandma's love of emojis to convey her appreciation of your ribald joke about cookies.
Email is a tool, and like all tools, it can be grossly misused and abused.
This is a client-side issue, IMO. If someone doesn't like HTML, simply don't enable parsing of it and view the source.
2. The bloat/ugliness argument could also be applied to websites, but no one is out there advocating for plain text websites.
In any event, email and Web sites are completely different things. Different communication mediums require different communication styles. Advocating for a certain style on one does not mean you have to also advocate for the same on another. The question would be "does rich-formatted text substantially add to the medium of email," and I think the clear answer to that is "not really."
An example of a good use of rich-formatted text contributing to an email would be coloring responses to questions. I see this one a lot, e.g. "my responses are in RED." We had the > quote style for this already, which was pretty good until an email thread started to get really, really deeply nested. In plain-text, at some point, somebody would have to edit the quotes down. There was a marginal advantage to having styled text to clear this up. Was this advantage enough to have to suffer through the majority of emails where this was not required and the formatted text was rife with extraneous or useless widgets?
I beg to disagree. Plain text doesn't offer any support for embedded metadata, which are vital for screen readers. With just plain text you have no way to tell apart a header, footer or aside from the main content.
> Web devs usually do a lot of work to make a Web site accessible.
Yes, they do a lot of work. Mostly using semantic HTML and embedding text descriptions in data attributes.
This should go without saying: Plain text is less accessible than well written, semantic HTML, not more.
The gemini folks (gemini.circumlunar.space/) basically are, but I think it's a similarly niche / reactionary take.
> "But if plaintext is so good, why is this page written in HTML?"
> This is a reference document, not an email, you twit.
They could have made this site plain text and followed all of their own guidelines, but they didn't. Instead, they wanted to make the site look prettier to get their message across with additional formatting plain text can't handle. They're reducing accessibility and increasing security issues just for their own superfluous desires.