It would be more useful to say that communities should be organised around a set of principles and be ruthless about sticking to them.

The issue isn't so much that groups become "political" (which is a hard standard to define) as much as they lost focus on a goal (like being a book club) and morph into an in-group, an out-group and a set of memes used to identify the in-groupers and ostracise the out-groupers.

The point of most political memes is to identify a small group who are coordinating to try and control a larger mass of people. When the local book club becomes a conduit for them that is obviously toxic for a general member joining because of the joy of reading. A book club community should prioritise books and including people if and when they enjoy books.