The military says they are a threat because they are too close to our airplanes, jets, and navy/air force fighter jets, helicopters, etc. And they have been spotted extremely close to passenger planes. I think the point is that if pilots could be informed that UFOs are real then they would be far less inhibited from reporting their sightings. Having spoken to a couple of military jet pilots, I've been told that seeing UFOs is far more common than people think, but they generally won't report what they have seen to their commanders.