Discussion culture in a forum … I’d go with “perceived” discussion culture. And for that, this forum is a glowing example of good behavior (compared to the Net in general, that is). Textual communication is always more complicated than one-to-one talk. Especially, if there are people with different language capabilities (not everyone, including me, is a native English speaker!), cultural and technical background. In general, people here tend to be nice, there are no ad hominem attacks and seldom snide remarks.
OTOH, I’m German: Opinionated, direct and not overly friendly. At least, I try not to whine all the time like some of my compatriots 
But cultural differences exist as well as personal preferences in communication style. We have to live with them.
As to what Markdown was, originally:
Markdown is a text-to-HTML conversion tool for web writers. Markdown allows you to write using an easy-to-read, easy-to-write plain text format, then convert it to structurally valid XHTML (or HTML).
In the words of its inventor, 2004. Since HTML is structured, I’d conclude that MD is structured, too. Of course, we have long deviated from that original state of affairs. I agree that many people consider MD to be a basic writing format. But in my mind, that’s stretching it a bit far. And from the discussions in this forum, I see many people stumbling over perceived shortcomings of MD or even DT (“How do I scale my images? Why can’t I click on the checkboxes?”) that are, I think, simply misconceptions.
I think that some use MD because it is simpler than Word, Pages, TeX, whatever. There’s not much to learn conceptually, you don’t need to start a huge program, all that. And then they, understandably, want to do more (images, tables, checkboxes, layout). That’s why we don’t have a single MD format nowadays but many dialects, some of them incompatible, some with “amendments” that make things more difficult.
That’s where we stand today: MD is ubiquitous, people like it and want to do things with it for which it wasn’t intended (like in the good old days when NeXT used PostScript for screen graphics – possible, but not the brightest idea). Consequently, there will have to be compromises. Especially, when we’re looking at a product that was not devised to be an MD editor. We’re looking at a small group of developers working on two products (DT and DTTG, not to mention Server).
I think they hear all the wishes for improvement. But they have to prioritize. And if there are dedicated MD editors out there that work perfectly fine with DT (or even DTTG), that’s fine for me. Being a Unix person, I do not expect one tool to do everything – having a working tool chest is important (again: for me).
As to my IDE/Debugger argument: MD is not in any way a preferred format in DT. It’s just one of many. Like for PDF, there are some functions to work with it, but not a fully blown editor. And a request for that is not any more legitimate than for a fully blown PDF editor (just take a look at all the problems people are describing here with the current PDF support due to PDFKit issues). I do store scripts in DT, but I wouldn’t expect them to be in any useful way editable there.
Interestingly, this just came up: Questions about editing word (docx) files
illustrating my point.
The debate is, BTW, two years old. Some things have changed since then. And I do not use DT for note-taking, just as a document management system. As, I have the impressions, do others.