His blog was prompted by a study by Robert McChesney and John Nichols that claimed the ratio of PR professionals to journalists in the US had risen from 1.2-1 in 1980 to 4-1 in 2010.
The article, along with a similar piece in the Financial Times, contrasted the growth of the global PR industry with struggling traditional media.
Greenslade concluded: 'What we're talking about here, as we chart the rise of PR and the simultaneous decline of journalism, is an assault on democracy.'
Nichols, the American study's author, went further: 'Journalism is literally being rolled over by propaganda.'
But this argument is simplistic. The growing power of professional comms is not causing the decline of journalism.
I should point out here that I see myself as a career journalist, and any decline in journalism is profoundly unwelcome. Further, I would argue that a true decline of journalism would also be devastating for the PR industry.
Journalists are losing their jobs because the traditional publishing model is broken. Papers are closing because audiences and advertisers have deserted them for online alternatives. Equally, the health of journalism in this country has been damaged by the actions of some tabloid journalists, which have left the public regard for 'media' on a par with that for estate agents.
Concurrently, business has gradually recognised the power of professional comms and shifted resources into this area. More recently - thanks to technological breakthroughs and possibly a symptom of weakened editorial - some firms have gone further, producing content directly for their audiences, circumventing the traditional media filter.
So while 'paid-for media' are in decline, 'owned media' - organisations talking directly to audiences - are booming. But 'earned media' are still where the real power lies.
Consumers still require third-party authorities to sort the wheat from the chaff - the truth from the claims. And few would argue that there is a lesser need for a 'fourth estate': a group of people that holds government, or any power for that matter, to account.
However, the nature of journalism has changed. It may require lower staffing levels. Power has shifted away from traditional media, towards new sources of authority, often peer review.
Good comms thrives alongside good journalism. Healthy democracy requires both to be honest and strong.