"That depends a lot of how you define unmasculine hair" It depends on how they defined it, or more narrowly on how they thought others defined it. You can't rebel against a norm if you don't believe it to be a norm held by other people, but you can rebel against it even if you don't think it should even be a norm (why else would you rebel?). So in a sense, perhaps the hippies weren't trying to be unmanly, but "unmanly".