The meta level issue is that they are assuming utilitarian morality. I mean, utilitarianism is that kind of high-brow value system one accepts after a lot of thinking and arguing, but it is nowhere intuitive. People and cultures who don't have that kind of value system simply see compassion as a weakness.

Besides empathy can get in the way of doing the right thing. A textbook example is doctors - many medically valid and necessary interventions or even examinations are painful. A basic simple colonoscopy means filling up a patient with air through the backside and for people who don't pass wind easily it can be the mother of all wind-colic pains.

Haidt has a well-known model of five various kinds of moral instincts. Compassion and empathy and utiliatarianism relates to one of them, largely the harm scale. Not even the other "liberal" scale i.e. equality or reciprocity is intuitively connected with it and the other three neither.

Also:

Research conducted by one of us, William A. Cunningham, along with the psychologist Nathan Arbuckle, found that when dividing money between themselves and others, people with psychopathic tendencies were more charitable when they believed that the others were part of their in-group. Psychopaths and narcissists are able to feel empathy; it’s just that they don’t typically want to.

This is historically normal behavior, because with high levels of scarcity you really take reciprocity seriously: you only give to people who have a significant chance of returning the gift. Psychopathy is largely up to definition. Do we really want to define it so? Do we really want to say all people throughout history who did care too much about the suffering of utter strangers were mentally ill?