Well, there would have been no coup if the Iranians had simply pleased the British and the Americans and obeyed them.
The United States after World War II decided to become the world's big brother, suggesting what kind of government was best for various nations. If necessary, it would encourage coups, as in Iran, Chile, and Vietnam.
Why blame only the CIA?
At the turn of the century, Mexico had a democratically elected president named Francisco Madero. The army did not like him. It wanted to overthrow him. The American ambassador said it would be fine with him. So the army did. It also murdered the president. Why? Because he tried to escape. Yeah, right!