[general_re]

I think he's saying why is it wrong for him to have that authority in his own country?

Because that "authority" is inherently and innately illegitimate, as Mill points out.

[GraniteStateConservative]

Did Mill advocate taking over every undemocratic nation and attempt to democratize them because freedom is God's gift to the world and we are the deliverers of that gift? You can agree that it's illegitimate, but deciding to go to war to liberate the world is a whole different issue.