Its part of brotherhood, when theres nothing to believe in, to take serious in, to believe strongly in, to be passionate and enthusiast about, then your bound to feel that way. Lets put it this way, for example with you being an athiest and lets say one of few living in a muslim country, outnumbered and not seen or met hardly any athiests.. youd feel a belonging with these athiests. Thats not to say its the same with religion. Religions are taught about brotherhood unity etc from the start, it really does depend how you see it from the other side.