May-19-2017 10:59 PM
In Alien Covenant, there is a scene where we see the arrival of the hijacked Engineer warship piloted by David and Shaw (who actually seems quite skilled at navigating the ship, while singing the American classic,"Country Road").
The scene opens to the C-shaped warship giving over a massive city. Below the ship, throngs of promethean men, women, and children cheer and welcome home the warship--why? Why would they be so jubilant you ask?
Well, one reason they may be celebratory is because the warship that Shaw and David arrive on was likely long-forgotten. Remember, the warships in the movie "Prometheus" were on a separate planet, a war-installation planet. The planet was known to the prehistoric populations of Earth (remember the cave dwelling art of the star constellations?). This means that the installation was likely thousands of years old.
Thus, one theory is that when Shaw and David arrived onboard the old relic--albeit unbeknownst to the joyous population below--that were given a hero's welcome. Moreover, the ship is seen conjugating or "synchronizing" with a larger, more advanced promethean vessel. Perhaps this is a cerimonial "red carpet" ritual for the warship, or perhaps it was simply a standard welcoming cerimony.
In either case, the ship arrived to a massive celebration.
Then--David, who at this point has been reassembled (a long process, that we can assume happened onboard the warship while traveling to the Promethean home-world) launches tens of thousands of the cylindrical, black, DNA-deconstructing tubules down at the unsuspecting planet.
The goo, which forms into a thick, black, cloud falls onto the city below, ripping apart the frantic crowds who scramble, and stampede (to no avail) to escape the destructive matter. At last, they perish, their bodies frozen in time like the citizens on the streets of Pompeii.
--With the scene set, the question becomes, why?--Why would David do that? He and Shaw finally arrived at a place where they could get answers--they finally found "the creators" of life--the answers to the origin of mankind, and then destroyed it without ever asking the burning questions.
**My answer to the question**
Near the climactic conclusion of the film, David and Walter are engaged in mortal combat. David, defeated, and now pleading for his life as Walter appears ready to destroy him, poses a question that is key to understanding "why" he did what he did--why he killed the Prometheans, why he killed Shaw, and lastly, why he created the "black" hybrid that we all know as the xenomorph. David asks, "would you rather serve in heaven, or rule in hell."
David knew, without a doubt, that if he were to interact with the Promethean race, if he and Shaw had descended to the planet's surface and met them, there is a chance that both he and Shaw would have spent the remainder of their years in the presence of intellectual superiors (in Shaw's case), or intellectual equals in David's case. As such, David would be nothing more than a common servant for them--just as he is for humankind--his creators.
Rather than live eternally as a servant to the Prometheans and Shaw, David instead chose to live as the "God" and king of the world. To use his own analogy, he chose to "rule in hell" rather than "serve in heaven."
To be able to rule in hell and to become an eternal God, he wiped out the Prometheans, killed Shaw (likely as part of the process of hybridization of the face-hugging xeno), and--equally important--he created life. He created something he hoped would be subservient to his authority--hence why he tried to "wisper" to the hybrid and get it to submit to him.
In short, David killed the Prometheans so that he could "Rule." David is imortal, and cannot die, in his opinion, he is a god--and all Gods must create life to cement their divinity. That is what he did. And the only way he could do that was by exterminating the ultra-advanced Promethean civilization.