What is hegemonic masculinity and why is it so important that we understand it?

What do these authors mean when they talk about masculinities and feminities? How do you make sense of the concepts of sexual identities, biology and desire? We all live in sexual bodies though our experience of what that means is incredibly varied. Why does sex cause so much trouble? How do masculinities and feminities work for and against the status quo to ensure that those in power stay in power? What is hegemonic masculinity and why is it so important that we understand it? Are some bodies less sex-worthy? Who should decide what kind of people are allowed to have sex?