Mainly you watch, your motivation is to not interfere and your belief is no one else should either. Leave things as they are

The Observer's Purpose

You believe the Earth should be left alone, but you are also interested in what happens here. Like a human nature scientist you believe much can be learned from watching things as they unfold "naturally."

Interference from other aliens on Earth will ruin your observations, by introducing outside effects. You work against these influences, but you are mainly a watcher.

Your path to "conquest" lies in having the Earth remain uninfluenced by outsiders (other aliens).

Stance in Conquest of the Earth

The Observer is here to observe, to watch, perchance to learn. To see, perchance to experience. The Observer is interested in what Earth is, what Humans are and maybe why they are.

The Observer is interested in keeping things the way they are on Earth, so that they may be observed and understand as they are. He may be actively engaged in defeating the more aggressive conquerors or "reformers." Even the Light Worker missions are not trusted by the Observer, for they too wish to change things.

 

How this individual Purpose mixes with a Species' Purpose

Observers, you might think, don't do a lot. That's not the case. There are so many other mission groups here that are wanting to change things, that these raise a threat to the Observer's mission, which is to observer things as they are on Earth, not as they might be, for better or worse.

Observers will work to defeat all other efforts, pretty much (save, perhaps, the Investigator -- though even they don't mind changing things). They will tend to band up with each other more than any other mission type.

They may be more aggressive toward the more aggressive mission types, such as the Harvesters, who just want to pillage the entire thing and move on to another primitive planet to similarly pillage. So the Observer says, "move on to another planet, now! (Or else)"