I think some people have trouble conceptualizing those around them as human. From what I can tell it’s not intentional cruelty, at least at first, they just struggle to conceptualize and understand the idea that all of the people around them have just as dynamic and complex inner worlds as they do. When it’s a struggle to make that connection, it’s easy to go through life ignoring the plight of those around you, disregarding them with the same ease most people dismiss a warning on a computer.