Why did David poison Holloway?

David has motives other than what weyland knows about. That he survives the movie, purely from a plot driven perspective, evidences that he has more to reveal. As regarding the 'insults' being a motive, that's interesting although I dont believe it was a motive in itself, that the movie highlights this tension and shows it to be at least a part cause poisoning points to some resemblance to reasoning beyond what David should be able to engage in.David certainly has an internal mind which Weyland does not intend to exist as it is beyond davids functions.I honestly dont think enough has been made about the very strong linking of david to Lawrence of arabia. The message of that film, that story if there is one lesson that jumps out of the movie Lawrence of Arabia, it’s this: it takes great talent to bring unfocused elements together for a great purpose.This 'great purpose' is what i believe motivates David.Simply, we do not know the motive.... all will be revealed.There are too many different perspectives its impossible to guess.David is equally 'Alien'