The Golden Rule got kind of expanded into the Kantian Categorical Imperative - instead of what one should do to be moral, it tells us what we should not do. So he says, "do not treat people as purely a means to an end, because they are human and have intrinsic worth" for example, don't lie, don't cheat, etc. Which isn't a bad way to live life. Of course, he said it'd be wrong to lie to an axe murderer the whereabouts of your loved ones on the grounds that it treats even the axe murderer as a means to an end rather than as a person... so not perfect anyway. Ideally, if everyone is following the Golden Rule or the Categorical Imperative then there is no harm ever done. But we don't live in an ideal world.

Socrates said "there is no moral evil" because he said it was impossible for anyone with sufficient knowledge to act in an evil way. Because, in his view, if they knew enough they would act in their best interests - which means limiting harm and never treating others poorly. For him that meant education and the cultivation of certain virtues meant people would act well instead of giving rules to say what is the right or wrong way to act - except his virtues were made up in Antiquity lol so didn't really include a lot of respect for women's rights for example.

Sometimes Justice and Doing What Is Right demands we get some retribution or are made whole after some harm was done (for example, being abused by a person in authority) or even act punitively to prevent future harm (like removing those teachers from their jobs, maybe even banning them from ever working with anyone vulnerable, not just children). In that case, it's wrong to keep treating someone well when they're harming you - it's only going to encourage further harm to someone else.

Maybe treating them as you would have them treat you might include "hey, if I'm acting like a dick and abusing people - tell me and others and do everything you can to stop me from doing that." Sure, that's "badly" for narcissists who think they can never be wrong but not for people who aren't, right? If I said something harmful carelessly, I would hope to be corrected! There's certainly a class of people who really think treating them "well" means doing whatever they say to do and accepting all punishment, earned or not. IMO, they have a very poor understanding of what being treated well really means lol