It's simple. My coop membership is worth a few thousand dollars a year in savings. If I weren't saving money, I wouldn't be a member. And I find Working there the required 33 hours a year is pleasant for me. If it became unpleasant, I would stop being a member.
In the September 8, 2011, Linewaiters' Gazette there is a letter from a member who complains(!) the management staff is doing "everything in their power to maintain their Co-Op as a food store and not as a social experiment or an activist force."
Well, it happens to be my Coop, too. And the management is doing exactly what it is supposed to do: keep the store well-running, so people can save money. Because I guarantee, when people stop saving money, they will stop being members.
We have lots of choices for places to buy groceries. We choose which store based on our own cost/benefits analysis. The Park Slope Food Coop is a grocery store with an unusual, perhaps unique, business model, but it is still a grocery store first.
We have many choices for engaging in "social experiments" or being "an activist force." Don't coopt the Coop.