The answer I expected, and largely disagree with. There is absolutely no guarantee that everything coming from an academic institution or that is even peer reviewed is worth a damn. It certainly isn't as likely as in the pages of a general interest periodical or a daily newspaper, but academics, and their institutions have been severely compromised, as you admit. The internet and competition for content has corrupted the academy like everything else in America. Historians who 20 years ago would have consider it their life's work to make a single well received presentation in front of 200 peers at a conference desire more. Today you need a mega phone and your CV is not complete without a popular publication.
I do not have a problem with popular publications by historians. It certainly does not make them less "professional". What good is a new take on Mary Queen of Scots or Anne Boleyn if you can only hear about it in Dr Retha Warnike's classroom? She wrote books on those subjects to educate and challenge the thinking of people who would never sit in her class or attend an academic conference. There are thousands of real historians writing for public consumption who are no less historians then academics in ivory towers. Anymore, because of stifling influences found increasingly in academic institutions, historians writing for public consumption outside of universities are more likely to buck conventional wisdom, be more creative and even more honest.