lol, be nice to the "Paranoids" ("newly evolved species").
It's pretty much this situation: You can't really disprove what they can't prove. You can try to dismiss what people claim they've seen in a few ways: (A) They didn't know what they saw (B) They saw something that wasn't there (C) They lied (D) It actually happened
Of course the "Paranoids" will say: "It's just something you won't believe until you see it for yourself."
I suggest you watch this Monte Python short film to avert your mind to something "more productive"