Why do Christians call each other "Brother" and "Sister"? It seems, to me, like saying "Gay Rob" or "Lesbian Julie" or "Bisexual Stephanie". I know there is a biblical history for it, but it seems to just serve to separate the [so-called] saved from the unsaved, and thus rub in their status. When you do anything that is 'Separate but equal' (black and white race bathrooms, or half the bus for blacks and half for whites, etc) that is a very likely outcome. A church is an obvious and acceptable distinguished group, because that's what they're for, like gay clubs. But when you leave the realm of specialized for specific reasons, then it encroaches on "better than you" type thinking.
My sister nearly had a heart attack when I first stopped calling our friend, and her god-mother, "Sister Senedra" and would instead simply say "Is that Senedra?"