Here's the thing. The whole driving force in the movie is Weyland and his desire to prolong life / regain his youth. He wants it so badly that he funds an enormously expensive expedition to get it. The whole movie then reverts to the standard BS about the robot having to be ambiguous and apparently scheming and at odds with the very people Weyland brought along for the journey to find the answers for him, so he could get what he wanted. All through the movie it's just the usual - android ****s with humans. It makes absolutely no sense.
Weyland could just have brought David and no one else. He clearly had no use for any of the other characters in the movie, so why were they even there? The two scientists who found the constellation? Why where they there? The geologist, the biologist? Anyone? David just ran along reading the jockey text, pressing all the buttons, making everyone suspicious of him, making sure no one was working together, scaring them and making them split up, infecting the humans, direclt endangering Weyland and his quest in multiple ways. For no reason.
Clearly, the two scientists were brought there for a reason, as well as the biologist and the geologist. It would be imperative to them working together to find the answers, and with David being practically an interpreter, should relay what he was finding, so the others would know and they made the decisions together that brought forth the discoveries. Having him say what those markings on the wall was, and then having Shaw or the others tell him to activate it, making it a group effort, rather than a one-robot-mission kind of thing completely unrelated to the people on the mission even needing to be there.
Weyland wanted life. He funded the mission... so why was he having David go solo and not utilize the minds he'd brought on the mission with him, working together to find the answer for him - working together would surely have found the answers quicker, no? Why did David on more than one occasion endanger Weyland and the whole mission? Why the whole shady robot deal to the whole thing, if he was in fact just doing exactly what Weyland had instructed? Why the disposable "who the heck were those guys" characters?
The story could have been an old man and his robot in search for more life. None of the other characters matters one bit to the story or Weyland's mission, seeing as he's pissing on them being there through David from even before they go on the mission.
When dealing with motivations and actions of characters... Weyland's actions just contradicts his motivation - he works against himself and what he wants... and you are left with gimmicks to imply intrigue, ambiguity and double cross, when in the end... there isn't any at all.
May I recommend you completely avoid anything by Philip K Dick, Isaac Asimov and about 50 other sci-fi writers.
lol:lol