Agression is what an alien knows best. Look how they are brought into the world, they rip through their host's ribcage and feed on the body. The first thing they know as a newborn is to feed to survive. Same goes as an adult. To kill is to survive.
Well i think it is kinda like they are agresive because they are kinda like animals but they need to be agresive to gain territory and to grow the hive ect so in a way they are agresive to suvive thats how i see it i was just looking for other opnions on this :D