With the weekend bobbing into view, Chris means to share a joke with his readers - of whom I am one of the most loyal. He's saying that it's pointless taking issue with newspaper columnists since they aren't paid to get things right but to echo the prejudices of the paper's readership. OK, to criticize someone just because they got something wrong doesn't butter any parsnips. Everybody gets things wrong sometimes. However, public discussion of issues that matter itself matters if democracy means anything - as I assume here, without argument, that it does - and criticizing the views of others, proposing counter-arguments, pointing out when someone has made a mistake and is reluctant to acknowledge or correct it, exploring their reasons for what they say and what they don't, trying oneself to meet the arguments of others, and yet more of the same ilk, is the very substance of public discussion.
As for journalists being paid merely to echo prejudices, I take this to be a lighthearted insult to the profession of journalism and unjust; it is based on ignoring better exemplars than those Chris must evidently have in mind. The fact that businesses have to give customers what they want would only succeed as an argument if there weren't newspaper readers who wanted something else from the papers they read than the confirmation of their own prejudices - you know, information, accurate news, compelling analysis, and so forth.
(I did once try to teach my cat to read but only got as far as the letter D.)
