Blogs are a wholly inappropriate place for back-and-forth discourse to happen simply because if I have a blog, it's my blog. It's not a discussion board. I inherently have the advantage, I control the conversation, and it's all about me. I have the ability to delete comments I disagree with. That's not discourse, that's an echo chamber.
I completely agree with Medium. Just because blog posts have historically had comments doesn't mean it's the right choice. The minute people accepted "pingbacks" as a valid form of comment was the moment comments died. V!AGR@ and P3N15 type spam sealed the deal.