From the blog post, which links to a journal article with the same name:

The status of cooperatives in Western Canada gave rise to one of the major points of divergence between the Canadian and British left in the 20th century. Whereas the U.K. Labour Party’s Clause 4 committed it to “common ownership of the means of production, distribution, and exchange,” which was generally understood to mean public ownership, the Co-operative Commonwealth Federation (CCF) in Canada distinguished itself by affirming a commitment to “social ownership,” which included both public and cooperative management of the economy. It was only much later, especially after the CCF was rebranded as the New Democratic Party (NDP), that unions came to play a more important role. Its primary impetus, in the early days, came from the cooperative sector – especially the tradition of mutual insurance among farmers.

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I have absolutely no doubt that cooperatives provide enormous benefits to their members (as I put it in the paper, “it is a truism that cooperatives are better for their members – if they weren’t, then their members wouldn’t be their members”). Thus there is good reason to ensure that the law is neutral between different organizational forms. We do not want people to be stuck transacting with a corporation when they could be better off organizing a cooperative. My point is that there are very few additional benefits, to society in general, above and beyond the benefits that are enjoyed by the members. Cooperatives are good for their owners, just as corporations are good for their owners, with the implication that neither is intrinsically better than the other. The appearance of superior virtue for the cooperative form is most often based on differential sympathy, and in particular, a rather striking lack of sympathy for investors as a constituency. If one adopts an impartial perspective, treating the economic interests of all individuals equally, there is no real basis for this asymmetry.

That’s the gist of the argument. The details are more complicated, which is why it’s a journal article and not a blog post.