Why be kind? Well, we can start with the basic precept that biologically speaking we want to live long enough so we can produce offspring which carry our genes into subsequent generations. Biological organisms that want to die go extinct rather quickly, and individuals who want to die don't really need to answer this question because it doesn't matter to them. If we're not kind to the people around us our chances of survival dramatically reduce. So while we ultimately are acting on selfish grounds what it produces overall is this sort of illusive altruism.