Markdown is a Perl script that converts plain text into Web-ready HTML; it's also a shorthand syntax for writing HTML tags without needing to write the actual HTML. Markdown has been around for a decade now, but it hasn't seen an update in all that time—nearly unheard of for a piece of software. In that light, the fact that Markdown continues to work at all is somewhat amazing.
Regrettably, "works" and "works well" are not the same thing. Markdown, despite its longevity, has bugs. But here, the software has an advantage. As free and open source (FOSS) software, licensed under a BSD-style license, anyone can fork Markdown and fix those bugs.
Recently, a group of developers set out to fix some of those bugs, creating what they call a "standard" version of Markdown. From a pure code standpoint, the results are great. Yet there was no surplus of gratitude. Instead, the "standard" group found itself at the center of a much larger and very contentious debate, one that's ultimately about who we want in control of the tools we use.
HTML is for browsers
The Web turned the whole world into writers. Never in the history of the human race have so many people produced so much text. The Web has not, however, turned the whole world into writers of HTML. If writing HTML were a requirement to writing on the Web, very few people would be writing on the Web.
Not that it's particularly hard to write HTML. Only a small subset of the hundreds of HTML tags actually end up in the average bit of text. Most of the time you can get by with paragraph tags, em, strong, and anchor tags for links. (And of course list tags—where would the modern Web be without list tags?)
In other words, it's not that hard to write HTML. But it is a pain.