“From the UFO crash at Roswell onward, witnesses and their families were often threatened with death if they talked.”
Hogwash. Jesse Marcel Sr. and Jesse Marcel Jr. (who happened to be a long-time member of this forum) talked about it for years and never mentioned any threats.
Dire threats against UFO witnesses are well-established. A famous sign at Area 51 even warns that “DEADLY FORCE IS AUTHORIZED.” During the Cold War, the local airport near where I lived also had a major SAC base with U-2s, B-52s, and nuclear bomb storage bunkers. The warning signs against entry there were much less menacing.