I'm not in any way an expert in this area, but here is what I see. I don't think the argument is that it's being said as "bad faith after the fact". I think the argument is that the approach was told it had fundamental flaws. Those were ignored / denied. People continued to invest in it and suck up all of the research and bright minds in the field. Decades later it still has those fundamental flaws and has taken over all other possible avenues of progress as it has all grant money and and the majority of all departments working on it.

It's more "you were told this is broken before. It's decades later and it's broken in the same way. At what point to you admit that this approach isn't working so try something else?" And the answer is "No, we're going to keep digging deeper".

Fundamentally, approaches need to be falsifiable. If your theory is "falsifiable" in the small scale but ultimately unfalsifiable in the large scale then it's is fundamentally unfalsifiable and we can't use it to lead experimentation.

It's a breadth vs depth search question. We've lost all breadth of search in physics, because a little ways back we stumbled upon a branch that happened to have a (for practical purposes) infinite number of subbranches relating to ways to roll up string dimensions. So physics is stuck exploring all of those sub-branches instead of backtracking one level and exploring any other parts of the tree.

The argument is that everyone is looking under the lamppost for the keys. After 4 decades of searching there, maybe it's time to search somewhere else. And the argument is made even strong when decades back they were told, "Hey, I didn't drop by keys by the lamppost. I dropped them somewhere else". And yet most people keep looking there.