I was purusing some of the books on Beacon Press. What I have noticed is that a number of the books published seem to have a bias towards social liberalism, especially New Deal liberalism or even sympathetic to New Left liberalism. If this is true, then does Beacon Press have a progressive bias? If a UU wanted to publish a book arguing the case for private-market capitalism, could that UU get his (or her) book published? What about a book arguing against a living wage or arguing the end of affirmative action?
I think you may be confusing book publishers and news organizations. Reporters and their respective news agencies, were supposed to be unbiased and neutral. I know that is the ideal and not the norm, but that is another topic.
Book publishers can pick and choose what they wish to publish. In the mainstream publishing business, it is usually based on what will sell the most copies, which is why many of the big box stores stock large supplies of books penned by shock jocks and talk show hosts, many of whom promoting some of the ideas you have raised.
The fact that Beacon Press is guided by a set of principles rather than the almighty dollar is something that lends it more credence, at least in my book. (sorry, couldn't resist.) I know at the onset that the selections found at Beacon Press will most likely lean more toward progressive or liberal thinking, because that thinking supports the principles.
But, having said that, I think if the author grounded his arguments for private market capitalism, etc., in those principles, I would think they should probably publish the book.
