> You'd change your mind about "everybody knows HTML" ...
Absolutely. You could've stopped there without any further caveats. The comment above I think is HN arrogance, assuming that the rest of the web is at a certain minimum level of tech literacy.
So many people post facebook updates or online comments and don't what what HTML is. I know someone (relatively young, uses the internet daily) who doesn't know what a browser is.
That aside, if given the choice, I would voluntarily use Markdown for comments all day long, no contest. For example a bullet/unordered list[1] needs so many awkward tags, whereas a Markdown list is much simpler, and much more intuitive for those who don't know HTML[2].
Well for reddit comments, the vast majority of the comments I typically make will make use of quotes, bold, italics or lists (the comments that include markdown), I use stuff like tables quite infrequently. So even remembering a small subset of the markdown will make my comments much more readable. I learn the features I use regularly, from reading other comments, that's how I picked up markdown originally.
I'm learning Python, I don't expect to learn all the features, hopefully I will learn a small subset, enough to be dangerous!
> Well, why not a WYSIWYG editor (similar to that on Stack Overflow) that generates HTML?
Absolutely, this is a good solution also. I personally like knowing the markdown features, I guess, but that's just me ;-) There is an extremely similar feature in the RES addon which allows live preview, not possible on a smaller screen though. It even includes a helpful list of markdown features for the newbie.
Little things like <em> or <i>, and browsers being very tolerant of appalling HTML, mean that a lot of people only sort of know HTML.
I do wosh that BBCode or Markdown had better standards.