> I think one of Markdown‘s biggest sins is how it handles line breaks. Single line breaks being discarded in the output guarantees that your nicely formatted text will look worse when rendered.

My experience has been the complete opposite. Markdown parsers that don’t discard single linebreaks (e.g. GitHub-flavored markdown) turn my nicely formatted text into a ragged mess of partially-filled lines. Or for narrow display widths, an alternating series of long and short lines.

Markdown parsers that correctly discard single linebreaks make sure that the source text (reflowed to fit a max number of characters per line) and the rendered text (reflowed to fit the display width per line) both look reasonable.