I noticed that in ROTF the decepticons make several references to the perpetuation of the species. Their main motive seems to be to replenish their species , with the colonization of the earth as a necessary sacrifice. So far the autobots have managed to: 1. destroy the all spark ( cybertronian life source ) 2. destroy the energon factory ( cybertronian food source ) both in the name of saving humans, but each at a great cost to their own species. Yet so far, all the decepticons have done is try to find a way to make more transformers. In the first movie megatron wanted to use the all spark; in the second movie, they wanted to use the energon machine to sustain and build up protoforms, and eventually more transformers. It would be interesting to have Optimus and Megatron argue this in the third movie. In fact they should. So far the autobots been very naive; ironically the decepticons seem to be the only bots concerned about the species. As megatron said "Is our species not even worth the death of one human ?"