Hmm...in response to Stalker's post:
Stating that all a xenomorph does is eat, rest, and reproduce is a very broad statement. After all, the same can be said for humans when you strip away the social structure. Humans are omnivorous, so to say that natural human survival does not involve the taking of lives is likewise false. In fact, almost any organism can be looked at in that light.
We've clearly seen xenomorphs interact and communicate with one another, so I wouldn't say it's too far of a stretch for them to exhibit social behaviors. To say what they do when they are not hunting prey is more speculation than anything else, but it's highly possible that, while guarding the queen and improving their own shelters, there is some form of social interaction.
The "perfect organism" does not need to be devoid of emotion. All carnivores take the lives of others, xenomorphs simply do the same thing. Any successful carnivore is equipped to deal a swift and successful death. It isn't accurate nor fair to state that they spend the majority of their lives hunting and killing, especially when we do not know the maximum capacity of a xenomorph hive, nor their behavior when that capacity is reached.
Humans clear land and kill organisms to expand and continue to reproduce. Xenomorphs simply do the same, but in a much more efficient manner.
Furthermore, when the humans did actually stray into xenomorph territory in each scenario, they did not escape immediately, or they were unable to. For example, in the film Aliens, Ripley could have just as easily fled from the xenomorph hive instead of moving further and threatening the safety of the queen. There was little, if any, motive behind that action other than the desire to hunt down and kill the source of an already dominant predator within its own territory.
Also, we cannot be sure about the situation with the yautja, either. However, you can't say that the act of forcing a mother to stay alive for centuries solely to kill her children time and time again isn't a monsterous act, especially when we clearly know that said mother both loves and cares for her children. If it were a human in that situation instead of a xenomorph queen, I'm fairly certain many more individuals would feel the same way.And thus I clothe my naked villainy
With old odd ends stolen forth from holy writ
And seem a saint when most I play the devil.