In Greek Iconoclast literally means "image breaker". It has come to mean one who attacks cherished beliefs, traditional institutions, etc. ...
i·con·o·clast[ahy-kon-uh-klast]
–noun 1. a breaker or destroyer of images, esp. those set up for religious veneration. 2. a person who attacks cherished beliefs, traditional institutions, etc., as being based on error or superstition.