> They are all as complicated if not more complicated than just writing HTML. They all have a bunch of rules and special cases. I'd rather just write in HTML which I already know.

I find that Markdown is significantly easier/faster to write than HTML and, more importantly, easier to read in its un-rendered form. To me (and presumably lots of other people, given Markdown's ubiquity) it's well worth learning the relatively small syntax.

Edit: Here's a quick comparison with a README.md from one of my projects:

Rendered: https://github.com/cespare/reflex/blob/master/README.md

Markdown: https://raw.githubusercontent.com/cespare/reflex/master/READ...

HTML: https://gist.githubusercontent.com/cespare/ad6c41aa28583cac8...

Three things I notice from this example:

- The verbosity of an XML syntax with HTML is annoying, particularly the need for closing tags. <code>xyz</code stands out as particularly verbose (compared with `xyz`).

- Having to escape certain characters like &amp; makes this HTML sample harder to read (this is more of a problem with technical/code documents).

- Automatic linkification prevents stuttering: <a href="http://example.com">http://example.com</a>