Is the Blackmar Diemer opening really that unsound?

"... I’ve seen more promising players lured into incompetence by this opening than I care to remember. The basic pattern is this - player learns BDG, tries to get it in every game, thus limiting his chess experience (and, since the opening isn’t good, he loses too many games, meaning that his rating stays low and he can’t get games against better players). Nobody who plays good chess plays this line, and nobody who plays good chess ever will. ...” - IM Sam Collins (2005)
https://web.archive.org/web/20140627031504/http://www.chesscafe.com/text/hansen76.pdf

I have achieved 2400 - 2200 at Blitz and Bullet so I would strongly beg to differ.🙄 There is no good or bad gambit, just a higher or lower risk of losing with it. I agree that it's probably not advisable to be played in games with a lose time limit, but I would even recommend it in fast paced games. I have had great experiences with it.
... There is no good or bad gambit, just a higher or lower risk of losing with it. ...
I imagine that some would consider "bad" to be appropriate language if the probability of losing is sufficiently high.
I have achieved 2400 - 2200 at Blitz and Bullet so I would strongly beg to differ.🙄 ... I agree that it's probably not advisable to be played in games with a lose time limit, but I would even recommend it in fast paced games. I have had great experiences with it.
I imagine that IM Collins was thinking in terms of slow games and one's progress in chess understanding.

Since you have apparently lived by IM Collin's philosophy, may I ask you what rating you have managed to achieve? Restricting or forbidding knowledge has never turned out well throughout human history. Preemptively advising people to stay away from an opening while going so far as to claim it would stifle their progress seems very questionable imho. The diemer gambit definitely has a rather narrow field of application, but that doesn't warrant this crusade type persecution.
Since you have apparently lived by IM Collin's philosophy, ...
I have not said anything about how I have "lived". I have no idea what your theory is about the philosophy of IM Collins.
... may I ask you what rating you have managed to achieve? ...
Do I need much of a rating to quote IM Collins accurately?
... Restricting or forbidding knowledge has never turned out well throughout human history. ...
In this thread, can you identify a specific sentence "restricting or forbidding knowledge"?
... Preemptively advising people to stay away from an opening while going so far as to claim it would stifle their progress seems very questionable imho. ...
"... I also applaud [IM Collins] for calling out the Blackmar-Diemer Gambit, which is unfittingly popular amongst lower rated players. ..." - FM Carsten Hansen (2005)
https://web.archive.org/web/20140627031504/http://www.chesscafe.com/text/hansen76.pdf

You continue to post random quotes, but have yet state your own opinion based on personal experience and knowledge of the game.
Well, since you have decided to specifically quote him and appear to be quite vigorously defending each of his major points, I assumed that you must be familiar with his teachings. ...
Can you identify a specific sentence by me that supposedly suggests that I am familiar with his teachings?
… Thus I was wondering how much you have benefited with regards to your respective rating. So please tell me what rating you have managed to achieve?
It doesn't seem wise to discuss my rating while you have a misperception about me being familiar with the teachings of IM Collins.
You ... have yet state your own opinion based on personal experience and knowledge of the game.
Is there a reason why I am obliged to do so?
... I have met IM Collins once, so he might be able to show the problems with it. Wish he'd put that analysis in his book rather than just telling everyone not to play it, though.
In my copy of the book, there is about a page (including variations) on the subject.

Play 10 minute blitz for the next few dozen of games doing your gambit.
Your rating will plummet.
A 3min "blitz" is basically a slow bullet game
Bullet chess is more akin to a video game than chess

Bullet chess is more akin to a video game than chess
Nonsense.
Anybody can play well with enough time, but it is only under serious time pressure that one's true skills and weaknesses are revealed. Blitz and Bullet games uncover the depth and level of internalization regarding both your general knowledge of the game and skill level.
It doesn't seem wise to discuss my rating while you have a misperception about me being familiar with the teachings of IM Collins.
I believe it is you who has fallen victim to a misconception. ...
Would you care to identify a specific sentence by me that expresses a misconception?
Colby-Covington wrote: … By exclusively quoting the opinions of these renomated players while failing to state your own, you are inevitably suggesting that you are both familiar and in agreement with them. ...
Not sure what you mean by "them". Have you abandoned the assumption about me being familiar with the "teachings" of IM Collins? I am familiar with the specific quotes that I have posted. I posted them because I thought that they might be of interest to readers here. I do not consider myself qualified to judge the correctness of IM or FM statements. I can, however, do some looking for indications of somewhat similar opinions (such as yours that "obviously in a 30min game one might be able to pick [the Blackmar Diemer] apart").
... I have met IM Collins once, so he might be able to show the problems with it. Wish he'd put that analysis in his book rather than just telling everyone not to play it, though.
In my copy of the book, there is about a page (including variations) on the subject.
… I'm looking at the book now. The mainline of his section on the Blackmar Diemar ends at move 7. There are two equally short alternative lines given for black on move five, and an alternative move for black is mentioned on move 4 with no analysis. ...
So you no longer want to describe IM Collins as "just telling everyone not to play it"?
... That's nowhere near enough to declare an opening unplayable. I realise the author is a strong player who probably has a much deeper understanding of the opening than what he put in the book, but as published the analysis is far, far too superficial to back up his sweeping claim, printed in bold after white's second move that "Nobody who plays good chess plays this line, and nobody who plays good chess ever will."
I imagine that an author has to keep space limitations in mind when deciding how much to say on any given opening. Many authors have chosen not to mention it.