A couple of things in response to some comments above:
1. Flag-draped coffins: You harass a bee-hive, you get stung. That is the bee's defence mechanism. I can't remember now if the coffins were from the ships or the Demolishor scene, but the ones in the Demolishor scene were the result of Demolishor's self-defence.
2. Scouts vs refugees: Ok, Demolishor obviously knew something big was coming, referring to the Fallen, but he also clearly feared the Autobots and what they were doing. His Bio talks about protecting smaller Decepticons in hiding. Sideways is a courier. Hardly top military targets.
3. Mercy killing: If he was beyond repair, that was not established very well. Frenzy gets dismembered several times and keeps going.
4. Intelligence: Demolishor says the Fallen is coming. What an opportunity to find out more! But instead, he is executed.
5. Changing sides: poorly handled in the film, but perhaps also something the current generation of TFs are not aware of. Jetfire refers to it, and he is ancient. Wheelie doesn't understand it when Jetfire reveals it. The current TFs may have been fighting so long they have forgotten that they could choose sides. The Fallen himself appears to be neutral. Prime (hard to tell how old he is) if he know, could have offered Demolishor the chance to defect. Poor Sideways, on the other hand, was shoot first ask questions later.
6. Politics: much of this could easily leap into a political discussions about the country that made this film, much like the much more superficial and media-friendly argument about the twins, but that is beyond this forum's scope.