If notepad were to support Markdown by giving it a nice syntax highlighting and niceties like clickable links and automatic list numbering, while preserving the monospaced font, then that would be great. But with rich text formatting it has all the pitfalls of WYSIWYG editors like accidentally changing the style of something, having "formatting typos" where you tried highlighting only part of a word before making it bold, using the wrong header type, etc.