Rangers aren't whacking each other because one opposes war. It was an ambush and shit happened. The soldiers there probably didnt want to see their fellow Rangers get hung out for it and unwisely tried to cover up and pin the death on the ambushing force. Bad judgement not telling the truth and creating a cover story, but there isn't any plot to whack another Ranger from within a Ranger battalion due to their position on war. That just cant happen there.