Originally Posted by pyan
It wasn't originally espionage - the anthropologist wanted to find out more about the natives with a view to dealing more fairly with them, the mining company top honchos were quite ready just to blow them away - but if there was a cheaper way of getting what they wanted...
I disagree. If you follow the movie's dialogue, you can see that the corporation greatly fears bad publicity. In a dialogue between the head honcho and the scientist, it is implied that an outright attack on the Na'vi would cause a PR
backlash on Earth*.
The attack came because Colonel Badass hijacked the whole operation. Selfridge tried to avoid this outcome for the longest time, while faced with the prospect of declining profits. Jake Sully's "You don't want this kind of blood on your hands" is an accurate statement. Recall that Sully was given yet another chance to solve the crisis diplomatically. When this too failed, Selfridge's pressured will was so malleable he fell victim to Quaritch's jingoism with ease: By acting swiftly, exploiting the Earth-Pandora communication time-lapse, Selfridge could solve the problem once and for all, and worry about consequences later.
I think there's a development within Quaritch as well, as the movie progresses. At first, he was satisfied with the infiltration scheme, it giving him the sense of influence and control he wanted, but he grew impatient as Jake Sully dawdled around in the Na'vi settlement. Quaritch is much more of a driving force than the corporation.
* Which also challenges the alleged "all humans are evil" message of the movie. Quaritch is the only person in the movie who needs to be evil for this plot to work out.