Counter-point: It depends on a decision made early in life. Whether that decision is influenced by observations or upbringing is irrelevant. As it stands, most people have not subconsciously chosen (follow it long enough and it becomes a non-absolute but pretty hard to break subconscious compulsion) to be this way.

As a kid, I had chosen this. I was treated like a person whose only purpose was to be taken advantage of, to be harmed for others' gain, from all sides as a result. Then I made the other choice due to pressure. Then I saw that causing harm is not all good for yourself like people pretend it is, so I rejected it hard no matter the consequence. The result was people kept crossing the boundary of decency and even crime, but nobody cared because apparently I made that choice myself and it was only natural. If such things are not dealt with, only the few crazy ones will choose empathy for more than what brings one gain in some form… because it is simply not worth it. Rather you need to abandon the concept of worth to really choose this to the end.

It is not so much the brain being wired for not feeling empathy (I'd argue that the hunan body is instead inclined to live a life the opposite of cruel; to be compassionate instead), rather when the pain starts, and stays constant (for years), it remains hard to hold on. The problem arises in not knowing how to deal with these things. Learning from observation while not knowing anything is an incredibly inefficient and painful method that also leaves you vulnerable, and the malicious love to target the vulnerable ones most of all. It is extremely difficult to hold on to such a decision, and those who make such decisions half-heartedly only give up, usually.

On the other hand, choosing these things makes one more capable in life than most humans consider possible (in modern times at least) in many things. The benefits of being capable are usually attributed to being better suited at something innately, but there is a reason that most people who are considered extraordinary geniuses in their fields, apparently inhumanly talented, are also kind hearted.