On a personal level, I very much dislike that comment.It's not justice being done, it's just revenge.
I don't like revenge. It seems patently illogical. Shouldn't 'justice' be the attempt to repair emotional andor physical damages done to the injured parties? How does reciprocating harm help anything? How can the infliction of harm on another person, no matter the cause, correct anything? If the infliction of harm is the problem, isn't it our duty to stop the infliction of harm, rather than perpetuating it?
I don't think 'revenge' should be a recognized legal motive.
To compare: A man is murdered. His best friend hunts down the killers and murders them in turn. He would be arrested as a criminal. (If you prefer, you can use a parent and child, or a married pair, or any other close emotional relationship.) The friend would be arrested as a criminal, and he would be a criminal.
In another universe, the same person is murdered, and his significant other takes the murderers to court. They are tried, found guilty, and executed.
The end result is the same, and even the process, to some extent--but in one, the significant other is a criminal, while in the other, he is--not necessarily a 'hero' per se, but considered to be an honorable person. Why is this? I don't understand.