The claim that cooperatives act irrationally (and the implication that they're less efficient) requires some factual data to back that claim up, otherwise it's just that – an anecdotal claim. Here's academic data to dismiss those claims:
> Labor-managed firms are as productive as conventional firms, or more productive, in all industries, and use their inputs efficiently; but in several industries conventional firms would produce more with their current input levels if they organized production like labor-managed firms. On average overall, firms would produce more using the labor-managed firms’ industry-specific technologies. Labor-managed firms do not produce at inefficiently low scales
Source: Fakhfakh, F., Pérotin, V., & Gago, Mó. (2012). Productivity, Capital, and Labor in Labor-Managed and Conventional Firms: An Investigation on French Data. ILR Review, 65(4), 847–879. doi:10.1177/001979391206500404
Similar results were also found to hold in an older study by Craig and Pencavel in 1995.