Abraham, Isaac, and extraterrestrials

Atheists, as well as "progressive Christians", commonly attack the binding of Isaac (Gen 22). One challenge is to ask, "What would you do if God ordered you to sacrifice your child?"

I've discussed this before but now I'd like to approach it from a different angle. This is not a uniquely Christian dilemma. It's easy to recast the dilemma in secular terms. 

For instance, many atheists subscribe to ufology. Ufology is basically a secular hobby. Indeed, a secular alternative to religion. The hope that extraterrestrials will parachute in just the nick of time to save the human race from its self-destructive impulses.

Suppose a secular ufologist begins to hear voices. The voice tells him that he must assassinate the president to avert WWIII. Unless he does so, the president will trigger WWIII, causing a thermonuclear exchange that will plunge our planet into a nuclear winter. Only high-ranking government officials will survive in underground cities, as they, or their descendants, wait for surface radiation to drop to hospitable levels. 

Should the ufologist act on what the extraterrestrial voices are telling him? Perhaps an atheist will say the ufologist should ignore the voices. Extraterrestrials aren't really in communication with the ufologist. Rather, hearing voices is symptomatic of psychosis.

Of course, a problem with this response is that a psychotic is in no position to make that evaluation. If he was in his right mind, he wouldn't be hearing voices in the first place. He lacks that objectivity. The psychotic diagnosis has to be made by a second party who is not psychotic. 

Insanity can afflict the religious and irreligious alike. So it's easy to dream of a parallel dilemma for the atheist.

Now let's vary the hypothetical. Suppose that SETI picks up an outer space transmission. This was clearly sent by an extraterrestrial civilization with superior technology. The message tells earthings that if they summarily execute one billion humans, the other six billion humans will be spared, but if they refuse to do so, the human race will be wiped out. 

From a secular standpoint, should we comply with the message? Many atheists espouse consequentialism. Taking the lives of one billion humans to save the lives of six billion humans is morally justifiable according to that ethical calculus. Do we dare to defy the ultimatum of the extraterrestrials, given a credible threat, backed up by their vastly superior technology? 

From a secular standpoint, how is that different, in principle, from obeying Yahweh's command to sacrifice Isaac, or Yahweh's command to mass execute the Canaanites if they refuse to evacuate Palestine?