HTML is not needed for attachments to work. If the government for example, banned all use of HTML in emails, people could still attach (non-HTML) files to emails the same way they do now. Therefore the comment I replied to, a defense of HTML in emails, is a bogus argument.
> The point is that attachments are needed to make HTML work.
They are not.
MIME headers are helpful for telling MUAs what the content (type and/or disposition) of a message is, but there's nothing from stoping mail clients from just putting "raw" HTML in the body of an e-mail message without MIME.
A browser engine is necessary to render an HTML email, and browser engines have large attack surfaces -- and in general they are very complicated, which makes them difficult to reason about.
Also, normies don't write HTML, but rather they depend on services (like Gmail) offered by corporations to transform their composition into HTML, which gives the corporations and avenue to track me or to try to persuade or influence me unless I want to respond by instructing my normie friend never to send me email.
In general, HTML email brings the privacy and security problems of the web to email.
Also, HTML makes email much harder to archive because an HTML document's legibility often depends on references (embedded in the HTML document) to files on the internet, and these references to online files tend to rot.
Some of us are tired of web tech spreading its tentacles everywhere, especially to technologies like email that were already useful and mature before web tech started spreading to them.
