There were times when he wondered how his actions looked to the wider universe, considering his habit of automatically acting to protect humanity whenever the human race was in peril in some way or another. Discounting cases where his opponents already knew of him and his history with Earth, did the invaders who identified him as non-human just see him as the person who ruined their plans, or did they regard him as an interloper who'd arrived on Earth 'first' and was now 'protecting his territory' before he took control himself for some reason?
Most of the time, he liked to think that he was working to protect humanity's right to develop independently rather than anything else, and he always tried to acknowledge their flaws while still appreciating what they did right, but he wasn't blind to their mistakes; he just liked to focus on other things instead…
Regardless, his current location marked one occasion where humanity as a whole was in the wrong, and he had no problems whatsoever with interfering to work against them rather than for them. The Na'vi might be a primitive society, but they had a rich culture and a broad history that didn't deserve to be condemned simply because Earth believed that it needed what this planet had to offer.
He knew that this attempted conquest would end with a Na'vi victory and most of the humans being driven off the planet even if he did nothing, but the resulting casualties would be too high for him to accept that as a first option if he could do anything to stop it.
Besides… with what Earth would face in the not-too-distant future of this era taken into account, anything he could do to give them more soldiers might help improve their chances later…
His thoughts were cut short when the door he'd been watching finally opened, revealing the people he had come here to see. Watching from his chosen vantage point, he smiled as he saw Jake Sully, Doctor Norm Spellman, Doctor Grace Augustine and Trudy Chacón make for Trudy's gunship; whether or not his larger plan paid off, those four needed to make it out before he did anything.
He was fairly sure that he'd prepared for all eventualities, but if things went wrong now, he had to be sure that those four were available to mount their planned resistance…
As the two scientists struggled to help Sully into his chosen gunship, a quick glance at the control room was all the old soldier needed to see when Colonel Quaritch emerged to take his shots. Before the man could advance further than the door, the Time Lord had drawn his own weapon and fired, neatly taking Quaritch's head off before he could start firing. The headless general fell to the ground as the rest of the soldiers in the control room rushed to get their own masks on, the delay caused by that action giving the gunship time to take off before another soldier could emerge.
As soon as the gunship was out of range, he tossed his gun aside and pulled out the Energy Accelerator he'd acquired for this purpose. Based on a similar premises to the Pulse Generator he'd used to shut down the Matrix on that colony world, this machine generated a large burst of energy when activated, but instead of shutting technology down, it actually boosted the machine's power reserves to such an extent that most devices exposed to it would explode from the sheer scale of energy being channelled through them. As soon as the stolen gunship was out of range, he triggered the Accelerator, standing back and watching as all the remaining gunships collapsed in on themselves as their engines experienced a sudden burst of energy that disintegrated them.
He would need to check back in for a while to make sure that nobody got it into their heads to try and just bomb the Na'vi from orbit, but he doubted that anyone would go that far; Earth just didn't have the technology to commit this many resources to a world that had already proven to be hostile and had just shown that it could fight back (Even if he doubted anyone would guess how it had managed to mount this kind of attack), and an orbital bombardment could just destroy the unobtanium they were looking for. With most of their advanced technology out of action and no way of calling for convenient back-up, Earth should conclude that it wasn't worth pressing the issue and decide to withdraw.
He knew that there was no guarantee that everyone would decide to leave, and wasn't entirely comfortable putting so many human lives at risk- particularly when many of them had only come here because it was their job rather than because they genuinely thought they were in the right, even if most of them believed that their actions would save humanity- but it was a smaller cost than what could have happened if Colonel Quaritch had been allowed to continue to wage his war. Without Quaritch to drive on the military, and with the official project leader lacking the necessary charisma and influence to really inspire anyone to want to keep fighting to claim Pandora, the example set by the 'traitors' should get enough people thinking about what they'd done to realise that continuing to try and get the unobtanium wasn't worth the effort.
In the end, humanity's worse aspects should convince them that it was time to back off; they'd lost so much already that they'd decide that the risks to their future weren't worth the losses they were suffering in the present.
On a wider scale, the Daleks were 'destined' to invade Earth in the not-too-distant future, and even if the broad strokes of the invasion had to remain the same, he could provide them with some additional soldiers to increase their chances of surviving what they were about to face. Even after the invasion had been defeated, 'unobtanium' would be the last thing on Earth's mind on top of everything else they had to worry about then. Besides, with all the Dalek technology left behind after his original incarnation and his companions destroyed their main ship, Earth would soon have access to far more power sources than they had at the moment, rendering the need for this particular mineral obsolete as they rebuilt.
It would take a while, but both Earth and Pandora would recover soon enough… and all he'd had to do was kill one man and sabotage a major operation that could have increased the number of human survivors of the upcoming Dalek invasion.
He could focus on the big picture as much as he wanted, but that still didn't make what he'd done completely right…