Assumptions...
Did anyone ask the members of this church group whether they were liberal or conservative?
Or is it just an acceptable stereotype that no liberal could possibly go to church? Or act selfishly? Or that a church group must consist of Republican fundamentalists? There are probably a hell of a lot of Democrats in my church, but most people don't talk politics there.
I'm assuming Mary Anne knows the members of her library group personally, so she would know what their philosophies and politics are. But maybe not. Maybe she never asked the "nice conservative lady" what her politics are, but simply assumed it from the fact that she attends church, and said something ghastly about paying for something you get.