[tommorris]

The point of Markdown is to abstract away the common HTML use cases in a markup format. There's plenty of HTML semantics where mapping them into Markdown would be both painful and unhelpful. Like, I'm probably one of a small number of weirdos who uses code, samp, kbd and var. Good luck turning those into blobs of memorable punctuation.

Sometimes I want to put custom attributes on links: rel and class, but also RDFa attributes like property and classof. Without the ability to make a link the old-fashioned way, you can't do that.

Markdown gives shortcuts for the common stuff and allows authors to use HTML tags for the fiddly bits that it doesn't optimise. Markdown without HTML fallback for the use cases Markdown doesn't optimize for would make Markdown fairly useless.

If you went the other route and tried to turn all of HTML into Markdown syntax, you'd have an unusable language. Including HTML is the least bad of the options, IMHO.