The Saying "Never argue with someone who buys ink by the barrel" has been attributed to dozens of different people over the years.
Generally speaking, it was used in a way saying that it was foolish to get into a fight with the newspapers, the most pervasive form of media of the day. Those Media Monopolies had vast amounts of power to frame the debate in their favor, and virtually no other voices could be heard.
Over Time, the Media has changed, with Radio, and then the TV Networks, but generally speaking the same talking heads, with the same opinions were the only things that the public could hear.
Now? You've got thousands of Blogs and other websites, Viral Videos on Youtube, Blogs, Twitter, Facebook, and who knows what else is coming down the road. Rather than Ink, opinions are transmitted by electrons being pushed around through computer networks and onto your screen. And More importantly than the Medium, is the lack of monopoly power by the mainstream media. There's more of us than there are of them, and they no longer have the power to shut us up and lock out dissenting opinions.
It's a whole new media world, and they should be afraid of those who can spread their opinions using Electrons By The Barrel.