Something occurred to me the other day. You take apart an alien machine or weapon, and what do you find? Copper wires, dry-cell batteries, coupled-charge devices, Polyvinyl chloride plastic - nothing new under the sun. Physics and chemistry is the same across the universe - its more of a social thing how technology develops - we had gyrojet guns, but the guys designing them took shortcuts and they never worked right.
The one piece of technology we simply can't recreate, is the faster than light drive that brought them to Earth. So far as I'm aware, no alien captured has ever admitted to know how it works.
Now think for a moment - what are the common explanations for the reanimate phenomenon? Well, discounting the spurious supernatural ones anyway - lets be reasonable here. Alien biological weapon, Human bio-weapon we were never meant to know about, nano-vac gone haywire, nano-vac gone horribly right through a government command to turn people into shock-troops, experimental nano let loose in the confusion after The Event.
All of these ideas have a grain of truth behind them. Nano-vac probably did start as a military project, and can keep soldier fighting longer, and even counteract certain special weapons and does require outside oversight. Certain diseases do alter negro-chemistry or induce strange behaviors.
But - all of them also have easy counterarguments. The government isn't that competent, nano isn't that resilient, retroviruses don't rewrite all the DNA.
However, what we don't have an argument against, is the idea that the alien's warp drive did this somehow. I know arguing from ignorance and uncertainty about how it works isn't good rhetoric. But, how can we prove that it didn't?