There is yet a way to salvage the Golden Rule. As I pointed out in the first post, the GR is a makeshift remedy for failing to realize that one is treating the other person poorly. It thus admits ignorance and proposes a simple way out. At the same time, it presupposes power and love.
Now any type of ethical rule-following is never an end in itself but is a means to character-building. Following rules is intended to create a routine, then a lifestyle, and finally a set and permanent character or personality. "Human virtues" are an intermediate step between "human duties" and "human actions." Duty is supposed to cement virtue which will then allow the person to seek narrow happiness.
Successful execution of the GR already requires a modicum of interest in other people and charity toward them. Following St. Thomas, call these "nurseries of virtue."
Following the GR is expected to increase those. For example, it impels a person to engage with, to interact with others. If one is a hermit or loner, living in his private-idiotic isolation, then the GR can push him into communion with others.
Again, treating others according to a rule is merely a proximate end; the GR has the potential to increase one's charity. This potential varies; e.g., both autistic and psychopathic persons will have trouble abiding by the GR; the former, because they do not even realize other people have minds and are like them; the latter, because though they do realize that, they do not seem to care.
Consciously following the strictures of the GR can thereby increase both one's power not to do evil and to do good and diminish one's hatred for others and increase one's love.
Update. Here is another way in which the GR can increase one's virtue. A con man, Smith, reasons: "I want to be trusted, so that I can scam people. Therefore, I should trust other con men." Since the conclusion is false, Smith must either abandon the GR or quit his job. If he is determined to abide by the GR, then he has no choice but to become an honest man.
But won't the new GR look like this: "I want to be trusted; hence, I should trust other people, including con men"? Now that Smith is a really good man, he could reckon as follows: "As a trustworthy person, I like to be trusted. If I were not trustworthy, then I'd prefer, for my own sake, not to be trusted so that my power to do evil would be lessened. Therefore, I should trust other trustworthy people and not trust con men."