It’s fine if you you’re not inclined to believe the claims of Grusch, or Corso, or any number of other people who have made more or less the same set of claims over the years. It’s worth pointing out, though, that the U.S. government lied, point blank, about a whole bunch of things that they now publicly claim were secret weapons tests. Our government fully denied the existence of any military base at the site popularly known as Area 51 for decades, until they just came out and admitted to its existence in the 90s. And they did so at least in part because of pressure from UFO researchers! If your evidence that any part of UFO folklore is definitely false is just that “the US government said it was [x]”, you shouldn’t be surprised if people don’t find that convincing!