No need to be a true-believer to be passionately localist?... I've heard those next-town-stole-our-madonna-in-1132 stories complete with grr grr grrrs from guys who I'd say set foot in church exactly three times in their entire lives: christening, wedding and funeral. So I'd say it operates essentially on the same principle as supporting your local soccer team?  Or being a hereditary "red" or a hereditary "black"  or "white" in politics?

"Ignoring moralities is always undesirable, but doing so systematically is really worrisome." Mohammed Khatami