Well Ridley did say David was going to be the lucifer figure right? If he and Shaw touched down on the engineer homeworld, head attatched, on a juggernaut warship full of bio accelerent, which was made offworld for good reason, David could see the chance of playing god himself by testing the black goo on the engineer race like he did with Halloway. If my theory on the engineer schism is correct, this will spell a horrible doom for the " good engineers" who allowed our existence to flourish. Hence why they never came back after 2000 years. Also, as evidence in a deleted scene from Prometheus, the Engineers seem to be much more formidable than us. If a flame weapon(possibly one similar to fire and stone?)were used here to stop infected members of the engineer race, perhaps the missing xeno husks are results of them being more vulnerable to fire, leaving no visible trace.
