These two guys seem to be spouting a few ideas about what they 'thought' was going on in Prometheus regarding the Engineers' motives. It's a pity that these ideas weren't implemented a bit more clearly and more logically coherent in the context of the actual movie presentation!:
http://www.youtube.com/watch?v=EvI_kYY2PLA#ws@3.00
Spaihts:It opens up that array of possible answers, which is horrible all along its scope because you might find that the answer is:
"You failed us in every conceivable way; we reject what you are, what you have done"
And it might actually be horrible in the opposite way:
"Oh nothing personal, time is up! We just ran this experiment, we need the world for something else!"
Lindelof:"It's time to throw out this Petri dish and start a new one!"
Spaihts:Exactly - it's the Douglas Adams answer!:
"No, we're just putting up a traffic circle here! Nothing personal at all!"