I liked Prometheus as well. I don’t know if they’ll make a sequel, but there’s a part of me that sort of likes leaving it unanswered. Why did the Engineers suddenly decide exterminate us after creating us in the first place? Great question. And I admire the courage of the scientist going back to the Engineer’s homeworld to ask them that very question. It’s a profoundly human thing to do. For me, it was certainly one of the better sci-fi films I’d seen in quite some time.
I also enjoyed Prometheus. It made me wonder.
“Why did the Engineers suddenly decide exterminate us after creating us in the first place?”
I have a theory on that one, and I think it’s all kind of suggested by the movie, in a roundabout way.
Most people, including characters in the movie, make some assumptions before they get to that question. First, they assume that the purpose of the ship going to Earth was to exterminate us, because it was carrying the black goo, which seems to be a weapon. They also assume that what the ship was going to do wasn’t the original intent of the Engineers from the very beginning, but that something provoked the response. I don’t think either of those assumptions is quite correct.
First, we see from the murals in the “head room” that the Engineers know about the xenomorph, and seem to hold in high, perhaps religious, regard. If you look closely, it seems as if there are two engineers being “sacrified” to facehuggers in the bottom corners, with a large xenomorph presiding over the scene. Wherever the black goo came from, the engineers knew that it was not strictly a weapon, but a mutagen that could alter and create lifeforms, and they knew that the lifeforms it created were specific to the hosts and methods of exposure.
So, the worms on temple floor exposed directly to the goo, the scientist who inhaled the goo, the scientist who was impregnated by the worm-thing, and the scientist who drank the goo, were all transformed in different ways. It was only once the face-hugger type creature was created by a specific vector, that the Engineer was infected and the result was a xenomorph. So, to get from goo to xenomorph, a specific infection vector had to happen with specific hosts.
Now, we know that humans and Engineers had very similar DNA profiles, and we know that humans infected with facehuggers produce xenomorphs, just like the Engineers. So, it would make sense to think that the Engineers created us, not for any benevolent purpose, but simply as substitute hosts for the xenomorphs. We were just engineered to be dumb livestock with similar DNA, so the Engineers didn’t have to sacrifice themselves to make the creatures they desired, for whatever purpose.
There’s no sense in breeding xenomorphs until you need them, since they aren’t controllable, so it would be counterproductive. So, why not just breed a planet of defenseless hosts, and when you need the xenomorphs, round up as many of them as you need and infect them?