This vision of Alinsky as an "institutional" organizer is inaccurate. Yes, he did organize institutions. But in The Woodlawn Organization and FIGHT in Syracuse many of those organizations were created by the organizers. Nicholas von Hoffman talked about the block and building clubs he created and then worked hard to maintain over time in TWO. If I remember correctly, Horwitt is very explicit that FIGHT was constructed in part out of made-from-scratch " organizations. In the organization he created under Alinsky Tom Gaudette in the Northwest Community Organization was officially made up of existing organizations but in fact used a more "organic" approach where Gaudette wandered through the community asking people for their "problems" and creating flash-points around them to train leaders and generate larger actions. The churches in NCO were at each others' throats half the time, so he organized "at" institutions like churches but did not organize "within" them. And Fred Ross in California created the largest number of Alinsky-related organizations out of the house-meeting model which explicitly rejected using existing organizations.
The institutional organizing approach was actually created by the post-Alinsky IAF cabinet. This focus like a laser beam on churches as institutions was an invention that post-dated Alinsky, and Chambers was clear on this. The founders of PICO and Galluzzo were BOTH mentored by Gaudette in non-existing-institutional organizing and came to the church-based approach later on. In fact, von Hoffman told me that Alinsky really disliked Chambers, in part, as I understand it, because Chambers thought like what Alinsky elswhere called "plumbers" who are trying to create static models for organizing. That doesn't mean Alinsky was right--certainly this isn't fair to Chambers. Organizing needs to understand that this model was created for a particular moment when churches had many more members. Organizing needs as a field, I think, to focus more on ACORN-ish approaches. Yes, the kind of organizing that organizes individuals or through "from scratch" organizations is more time intensive AND may not organize as many people sometimes. But it does reach out to the non-churched, the lower income, etc.