NOTHING can fly in the air and exceed M1 without causing a shock. This is a basic property of compressible fluids and will not be changed. Something moving through a gas pushes the gas aside. If the speed is less than the speed of sound in the gas, the gas close to the vehicle has a chance to inform the gas farther away that something is coming. If the thing is moving faster than the speed of sound, the gas farther away cannot know that something is coming until it's crashing in.
Basic, basic high speed compressible flow, simple third-year undergraduate stuff.
Maybe they need to apply a little science to the problem.
They need to say "no UFOs are alien spacecraft" instead of claiming that maybe some are. Then with the negative statement in hand, a real theory, they can set about disproving the theory, which is how science is performed, and finding and proving the one case where a UFO is a genuine alien vehicle.
Once they do that, they have earned credibility.