I read in James R. Hansen's biography of Neil Armstrong about Armstrong's response to hoax believers who contacted him. Strictly speaking, this probably doesn't count as a NASA response because he's been retired from NASA for many years, but anyway, his aide would send them a letter that briefly summarized the reasons why the hoax theory was invalid and mentioned that Armstrong was offended by the Apollo 1 accusations and had spoken to FOX about this. I think this is an appropriate response. If someone says something about you that is not true and you state your case to them, if they still don't believe you after that, it is their problem, not yours.

I can see why NASA doesn't sue people over the Apollo 1 accusations, even though they are extremely offensive. This would just lead to the murder accusations being repeated in court transcripts and the media and NASA clearly doesn't feel like giving more exposure to these people.

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"One does not require alien ruins in order to absorb a profound sense of wonder and mystery from the moon. That our civilization had actually visited it is miracle enough." Jason Roberts