It's part of our evolutionary heritage to live in close, tightly knit groups that rely on each other for survival. It is in villages and tribes that our psyches prosper. We, in the Western World, are an alienated society with very little or no community ties. Almost any well adjusted group could provide the sense of community that most of us crave for.
It's a pity that the Watchtower and other poisonous religions take advantage of that inborn need to belong to something.