Why can't everyone just respect other people's beliefs and keep to themselves?

Most atheists have this superiority complex where it seems like they take pleasure in belittling the "stupid religious people who believe in unicorns and fairies". And then you have religious people who can be just as bad and say things like "You're going to hell" and all that. I think EVERYONE (Yes, even religious people) should keep to themselves about their beliefs unless they are asked to present them. When they do present them, it should be in a respectful and kind manner, I mean we are human beings after all, we should act it.