While we're at it let's get rid of streaming HD video and all that cumbersome CSS and Javascript (it just slows down page load times, and why should websites be dictated by the owner's sense of design?).
When you hand the design reins to everyone, you end up with Myspace profiles and Geocities sites. There's nothing wrong with either of those, but context is essential. When I'm reading through dozens and even hundreds of emails a day that are crucial to my daily work, I really don't want to have to deal with Paula's pink hearts theme or Bill's Boston Bruins theme. There's a time and place for everything. I do want confidence that I can read my emails quickly and easily, and plaintext makes that promise a lot better than HTML does.
Personally, I prefer the HTML emails and find them faster to go through. It takes me about 2 seconds to skim a Thinkgeek mailer with product images and see if there's anything interesting, vs. having to actually read the entire email and click a bunch of links.
Then there are all the nice graphs and colors in the server monitoring emails I get that let me get a big picture overview of the server farm health at a glance every week. If I see any red or too many spikes, I can decide whether to investigate further or get back to coding.
For all the benefits I get from HTML email, I'll risk the small chance that getting an email with Paula's pink hearts theme will seriously fuck up my day.
And for sure, you do make some good points on where HTML email can be a good thing. Perhaps I'm being too pessimistic.
Much much worse, however, are all of the people/companies that include multipart/alternative sections, but do it completely wrong: "This is an HTML-email. Your client lacks HTML support. Please visit [url here] to view this email" or even worse "This is an HTML-email. Your client lacks HTML support. Please upgrade your software".
I come across these almost daily, and it bugs the hell out of me. Unless it is something very important (bill, sign-up email, etc.) I simply ignore these emails, and they never get read. (Yes, it really is out of spite. I'll ignore them when reading email in a web client or on my phone later. They simply lost their chance)
I don't really like HTML mail, but I can live with it. I see the reason why it exists (great for advertisement). However, if you use HTML email, do include multipart/alternative section for non-HTML clients, and include the same information there, non of this "your client can't handle HTML, you loose crap".
I can't find the option in Outlook 2010. It's made working through my inbox more frustrating then it need be.