Earlier quoted context omitted.
It has nothing to do with literacy, the em-dash simply is not on the standard US QWERTY keyboard. This means that people who purposefully use it, either have to copy-paste it from somewhere or (if they-re on Windows), use "Alt + 0 1 5 1". This is very obviously not a natural behaviour that 'literate' people use when they write.
You can type "--" in most writing software and it will turn into an em-dash. On a Mac, this includes TextEdit by default, or literally every text input field if you enable the "smart dashes" setting. I can type — right now in my web browser with two presses on my ordinary laptop keyboard and no memorizing character ID numbers, not exactly rocket science. If you're using Word or other fancy word processors, you don't…
Probably not, this is "HACKER" News, if I type two n-dashes on a website, I EXPECT two n-dashes, otherwise things like HTML comments would break the page.