First, "conspiracies can't be true" was definitely not the point. You're right, conspiracies happen, governments
do keep secrets! The point was: if a conspiracy theory
with poor evidence were to be a reasonable explanation for another claim's poor evidence, I could claim whatever outlandish thing I wanted, e.g. "Unicorns are real, our puppet masters just don't want you to know about them!" This explanation is hard to falsify, and (in my view) shouldn't be our top choice, it's definitely not enough for me to regard the ultimate unicorn claim as "well-established fact."
If I wanted to make a compelling argument for my conspiracy theory, I would not only want to explain how the government has managed to keep this profound secret about unicorns, I'd want to to explain why it was theirs to keep in the first place. In a world with many sovereign nations with a vast array of publicly and privately-funded research institutions, camera-toting citizens, security cameras, wildlife cameras, etc., why is the U.S. government holding all of the compelling evidence? Or is not just the U.S.? Maybe we explain this with more conspiracies? Or maybe one really big conspiracy? Do you think it's likely that the government could keep narwhals a secret?
I haven't/wouldn't make any claims about David Grusch being who he says is, I haven't intentionally made any truth claims at all here; that said, whatever titles Grusch formerly held, and whatever title his lawyers formerly held, those titles don't, in my view, grant him credibility in perpetuity, maybe one could argue that they didn't grant much in the first place. The same goes for members of Congress. Should we believe Marjorie Taylor Greene if she tells us "The Jews" are starting forest fires with their space lasers to serve their malicious globalist agendas, on the basis that she's a congresswoman?
If you or anyone else has evidence, I'd urge them to be agents of truth and go update Grusch's Wikipedia article, at the time of writing this it states:
> No evidence supporting Grusch's UFO claims has been presented and they have been dismissed by multiple, independent experts.
Or, perhaps we go searching for explanations as to why Wikipedia or the news organizations it accepts citations from are mere puppets of the conspirators, but at that point, who's being tiresome?