Because the Decepticons are the bad guys, people normally think of them as the ruthless ones. It's true, they do obviously care less about innocent lives than any of the Autobots. However, it's also true that the Autobots have been at war with the Decepticons for millions of years. It's safe to say without a few rough-and-tumble 'bots, the Autobots wouldn't have stood a chance.
Source：https://www.cbr.com/ruthless-autobots-transformers-comics/
