"A competent text editor (let's say no older than 40 years old) can highlight and/or render that"
But I'm not EDITING them. I just want to double-click on it and read the document, rendered properly. I do not want to have to open it in an editing environment and then invoke a preview (which often takes double the screen space). Again, WTF is up with the lack of lightweight, dedicated Markdown viewers?
I don't agree that stuff like ## and `` all over the place is eye-catching and attractive formatting. It's absurdly regressive. At that point, why not just use RTF, for which there are built-in viewers in the dominant OSes? Or if you really want plain text, use indentation, spacing, and capitals to organize the document.
If OSes' default viewers (like Notepad in Windows or Preview on the Mac) would render Markdown, I'd be fine with it. But they don't, and if they haven't added it yet, it doesn't seem that they will.