The problem of deniability and "disavowing keys" is subjective and requires technical skill to understand, that average person will not find this "equalization of legit and forged data" intuitive and will believe that keys/signatures/encryption on content adds authenticity on equal level with "legit data" - instead of "repudiation" you have a 'weak proof of authenticity' that could be disproved later(the burden of proof shift here is important psychologically since keys/encryption are perceived as legitimizing content).