Those are interesting claims, but first I’d have you admit you were wrong; there is a consideration of empathy in Johnson’s writing.

We are now farther afield from the origin of this debate than is probably productive; but I like talking about morality, so why not?

You certainly must have the right intent in order to act morally. The landslide which kills a thousand people is not evil, and the person who saves another from a burning building in order to rape them to death has not done good. But it’s not clear from this that empathy is necessary for moral acts to exist. A man may believe that there is an inherent rightness or wrongness in the universe apart from his own understanding, which he must strive to abide by because “what’s right is right.” This is common in religious morality; people act morally within these systems because they are striving to do good in the eyes of the universe, not themselves or others. Similarly, there are people who may believe that the mores of society comprise their morality; one can imagine a police officer who smokes pot recreationally at home because it is not considered wrong in the eyes of society to do so, but who arrests pot smokers at work because it is considered morally right by society for a police officer to perform the duties they are hired to perform; for that policeman, there is no cognitive dissonance; he is acting morally within his own system. Yet were he to place himself in the shoes of his pot-smoking convicts, he’d feel persecuted. His morality exists apart from empathy. These moralities may certainly be flawed, but determining the right system of morality is probably beyond the scope of what you wanted to discuss.

Perhaps more seriously, when one claims that empathy is necessary for morality, one removes the possibility of morality without interaction with others. For example, under your claim it would be impossible to act in your own interest, because there is nothing to empathize about. You might try to claim what makes an act of self-interest moral is the actor’s ability to imagine another person performing that same act and finding it good for that other person to do so. That, however, exposes the problem that empathy itself relies upon an external measure of what is “good” or “bad” for a person — if I go on a diet in an attempt to prolong my life, I might imagine another person doing this as well in an attempt to evaluate whether or not I am doing the right thing. But it would only be good for a person in the same mental state as me; a suicide would find it repulsive, as might a hedonist.

Empathy exists as a tool within the toolkit of some moralists — but not all! and it does not itself create a fully-functional moral system. Rather, it necessarily exists within an independently-derived moral system from which it gains its force.