From the start, “Mad Men” has, in addition to cataloging bygone vices and fashion choices, traced the erosion, the gradual slide toward obsolescence, of a power structure built on and in service of the prerogatives of white men. The unthinking way Don, Pete, Roger and the rest of them enjoy their position, and the ease with which they abuse it, inspires what has become a familiar kind of ambivalence among cable viewers. Weren’t those guys awful, back then? But weren’t they also kind of cool? We are invited to have our outrage and eat our nostalgia too, to applaud the show’s right-thinking critique of what we love it for glamorizing.