The worst abuse that I have seen was in situations in which someone decided that somebody else was a bad person. There are ways to deal with this problem.
If this happens in a relationship, then the solution is to call his bluff. It is to say, “If I am so bad, why are you with me?” If you really were a bad person, he could not wait to leave you. If he chooses to stay, it is because he is getting something out of the relationship. And if you are getting something out of your relationship with another person, then you are obligated to be good to her whatever you believe her character to be.
If this happens outside a relationship, the solution is to make the person not credible through your actions. It is to observe high standard of conduct, making his accusations not credible. Do not defend your actions to that person; that would only give him more to pick on. Rather behave in an honorable manner, and his accusations will be shown for the folly they are.
It has been said that people are never so vicious as when they think they’re righteous. The antidote to viciousness done in the name of righteousness is to show it to be unrighteous. If a man does this in a relationship, he needs to be told that for as long as he is getting something out of a relationship he must be good to his partner whatever he thinks of her character. And if someone fixates on another – as has happened to me for a number of years on the Internet – he needs to be told that he is not the military or the police, and it is not his place to persecute another person.
Of course abuse done in the name of righteousness discredits righteousness itself; and this then feeds unethical conduct. People identify the cruel behaviour with the values for which it claims to speak. This then leads the more compassionate types to turn against righteousness as such. This results in a paradoxical situation in which the better people do not believe in morality and the worse people do. And that is bad for the world.
Abuse in the name of righteousness is just that: abuse. The ends do not justify the means; both the ends and the means are judgable. The people who abuse in the name of righteousness discredit righteousness, leading the kinder people to turn against the concept. The solution is to do away with unrighteous behaviour done in the name of righteousness. That way the value will not be identified with the abuses of the value, and value itself will be preserved.