You mean rejecting an explanation based upon lack of proof for something which itself lacks proof. In both cases the subjects seems to be "camera shy," making if difficult to provide clear visual or material evidence of their existence, and with most of the testimony being anecdotal. And in any case, with all of the proffered evidences being dismissed by skeptics as explainable by natural causes.
But for those who find warrant for the Bible being true, and or have seen evidence of the supernatural (whether it be testimonies of the providential and miraculous workings of God or such manifestations as the surgeon of the rusty knife ) may not find the spiritual explanation of UFOs implausible.
If the requester is asking for a Thomist-like philosophical or theoretical blow-by-blow analysis, I'm still the wrong guy; it'd be akin to a little leaguer trying to hit Nolan Ryan.
HAVING SAID THAT, the most PLAUSIBLE argument I've read is something like the following:
-light-speed travel (as we envision it) is fraught with peril...the devastation if you hit a tiny piece of rock grows as your speed accelerates. Thus a pebble kicking up and hitting your windshield at 55mph may cause a crack; at light-speed your space craft is destroyed. So, compound that probability of a piece of space debris being in your path across scores of light years.
-demons are fallen angels. They really don't like us. In fact they hate us, but they are sneaky and understand us better than we know oure lives. They know our Achilles heel.
-(fallen) angels are spirits and not subject to material limitations so the aforementioned light-speed problems don't apply to them.
So, logically then...if there are simply too many UFO sightings and pictures etc to blow it off as Swamp gas, AND if it's physically unlikely for aliens to survive travel across the vast distances of space, AND if fallen angels hate us and want to destroy us, AND if they know our fascination with aliens, AND they can travel from here to there without limitation...
AND therefore...