One of the primary reasons email sucks is the allowance of "text/html" with no text/plain part, or worse, something like "Turn on HTML" as the text/plain part.
I display my email as plaintext for a few good reasons: first, because software is generally shit, they reuse a web browser component which was never intended to be used with email. Result: you suddenly run javascript, load remote images, etc. Pretty much anything email should NOT be doing.