Masciotra is best known for writing a fawning biography of has-been pop star John Mellencamp. He is obviously a far-gone media culture conformist, "media" to include the entertainment media. While he apes leftist attitudes in this piece, it is missing the point for anyone to call him a "leftist." He will, like all such conformists since the 1960s, advocate whatever position most glorifies the corrupt values of the media culture. The latter, of course, is ultimately based on the requirements of the advertising industry. Since most advertising since the 50s has been based on false contrarianism, someone seeking status within that culture must also take a superficially contrarian position. Tell-tale signs include the broad generalizations, barely concealed snobbery, and self righteous tone of such work.
For more on this subject see The Conquest of Cool, Thomas M. Frank's damning expose of the historical relationship between the advertising industry and leftist culture and politics since the early 60s. Among other things, Frank demonstrates that ad agency Doyle, Dane, Bernback essentially invented the "youth counterculture" ("hippies") in the mid-60s (though they did not actually coin the term "hippy.") That Frank himself is a lefty, though a real one, only makes his message that much more credible.
I haven't read the book about the advertising industry, but I sincerely doubt an ad agency created the hippie culture. The forces of time, societal pressures, and circumstance are responsible. Did ad agencies try to cash in?...sure. But created it....no.