I am certainly not someone well versed in the area of psychology, as I have only a lay understanding of many if not most aspects of it. But when you say there is no proof of empathy being the source of altruism and the lack thereof being psychopathy, is that your interpretation, or more of a fact?

I am also not an expert in the field of psychology. In this reply, I was speaking more as a skeptic. When I posited that there's no proof that altruists feel empathy, I was looking for some hard concrete proof that was objective, like a brain scan or something like that.

Without that, it's just the person's word for why they're doing something. For instance, there are numerous articles or posts that question whether Mother Theresa was a sociopath or a psychopath. On a quick search with the keywords Mother Theresa and psychopath, here's one, and another one and the article mentioned in that post. Penn and Teller did a TV show where they say that

Mother Teresa a religious zealot who was happy to see the poor suffer.

However, she has been acclaimed as one of the biggest altruists. She has become the exemplar for altruists.

Yet, there's no real proof that she had real empathy for people, and some people claim she had none.

Conversely, while the definition of psychopaths is that they don't feel empathy, there's no proof of that either. When someone does something against society, they're often called psychopaths. In order to give a reason for how they could do something that most people wouldn't do, the reasoning is that they didn't feel empathy as others do. They themselves might say they didn't care about what happened. But often people can do cruel things to others because they've either justified it to themselves or because they've blocked out the part that cares about it. That's doesn't mean they don't have empathy at all.