How does your browser render that? This isn't something unique to emails, and we didn't end up deciding that text only web pages were the way to go. That said, email clients could catch a number of simple cases like that and warn the user (yes, I realize there are ways around that).
> If you can't get your message across in a plain text email, you may want to reconsider whether your intent is to mislead.
While this is true, the reality is that html emails are, basically, required in many cases due to marketing. Generally speaking, html emails are not being created by legitimate business because they want to mislead people. They are being created because they look better (leaving aside the caveat that some businesses aren't very good at the "make it look better" aspect).
As for "look better" - yes, it is subjective. However, given that html email capabilities are a super set of text email capabilities, anything you can do in a text email you can do in an html email. Anything you can do in an html email, though, you cannot necessarily do in a text email. Quite simply, an html email can look better and often does.
Edit: Given that an email can contain both text and html versions, and given that best practices dictate sending both, is this not good enough? You can always set your client to show you the text version by preference. You get your text version, most everyone else gets the html version.
Yes, text-only emails make things much simpler from a security standpoint. Text-only websites were also much simpler from a security standpoint.
The problem is that marketing wants designed emails to the customer that catches the customer's eye. For the most part, plain text marketing emails end up TL;DR.
Multi-part mime types for a html and a text email for those of us who don't read HTML in our email :)
(I love plain text email, but this proves too much.)