The UFO universe would later become the Star Trek mirror universe

Just think about it. Stripperiffic outfits? Check. Dark themes? Check. And then there's talk of a unified Earth - so they can fight other planets better. If, say, a spaceship landed there, in 2063, and all of UFO's history with "shoot first, dissect later" had gone before, it'd be pretty much a natural reaction to shoot the newcomers (you know, before they get to use their newest secret weapon) and loot their ship.
(This is a WMG with emphasis on the "wild", just so you know...)