The reason people sometimes need to be "unkind" is to prevent some cost from being incurred. (Another conceivable reason is personality disorders, but let's ass

The reason people sometimes need to be "unkind" is to prevent some cost from being incurred. (Another conceivable reason is personality disorders, but let's assume normal healthy people.) For normal healthy people, kindness is the default state when it is free. When there are costs, it becomes a luxury only some people can afford.