[saidajigumi]

No, of course not. While Markdown is plain text, it is a markup language with its own syntax. This syntax is parsed by tools to transform Markdown into other formats. As it happens, this is analogous to code: encoded as text with a specific syntax.

As such, "markdown editors" are for the most part text editors with syntax highlighting. The syntax is important because it encodes the user's intent beyond the raw text bytes. Just as with code editor's highlighters, we use them because it provides an immediate and useful visualization of our intent. "Why isn't my link highlighted? OH, missed that paren." "Why is everything italic? OH, fat-fingered the closing asterisk."

So while well-formatted Markdown happens to also be well-formatted plain-text, but that doesn't mean that good authoring tools aren't needed or helpful.