The Ending Explained Differently.
Many that didn't like the ending seem to be in disbelief that it would have happened like that, but after a couple of viewings, this is how I see it:
After they sat in the truck when the fuel ran out, the impending noises of the creatures, and the sound of the incoming military, which would have sounded scary as hell without knowing what it was, rushed them to conclude that they would rather die quickly rather than by the methods they had previously witnessed. This theory is backed up by David leaving the vehicle and yelling "C'mon!", expecting the creatures to finish him. The incoming noises they all heard rushed them to judgement and I think many people, if not all, that had gone through all that fear and stress, would probably prefer a bullet to the head instead of being torn apart. I don't think a discussion would have been necessary. I think if they weren't as scared, and they sat in silence, the instinct to survive would have kept them in the truck with hopes of a different outcome.
This makes perfect sense to me.