Let's start with some definitions and axioms and predicates and blah blah blah, since a lot of morality discussions get lost in the weeds of definition games and arguing semantics:
- Actions undertaken should be worth doing.
- I define worth doing as having greater utility than other choices you're aware of and able to choose, including doing nothing.
- I'm not going to define utility exhaustively here because it's not worth it

- You have to account for externalities, not just your own immediately outcomes - society, reputation, etc, blah blah blah.
- If you care about other people and society, which I think you should, this does mean that if your life is ruined, you might have a reason to deal with the life ruiner lest they do it to others.
The worthiness of revenge in a moral sense
should be a matter of what is a good idea for everyone to do, including you, your friends, other random faggots, and even your enemies. Moral actions should be what everyone does, to everyone else, including you. Sadly, we are not in Kant's heaven, and most people are stupid, selfish, lazy faggots. Most people will act according to their selfish, lazy stupidity, so we need to figure out how to do what's best for us and the society around us, accounting for the fact that many if not most people are going to just be selfish and shortsighted.
Being overly selfish is self defeating. Having a bad reputation, attracting the wrong kind of attention, destroying your society, etc, leads to a worse outcome for you. So clearly you need to avoid that to actually maximize your own utility. So even selfish people should work together with other people because it's better for them in the end. Where that point lies is worth a few Ethics PhDs and beyond the scope of an effortpost on revenge.
Arguments to only work through the legal system fall apart the second the system fails, which is constant. The fact that the system is also a pay-to-win system further undermines it. The legal system, and indeed a government saying "be docile and just do what we say and ask us to step in for you" is the government, and especially the judiciary, saying "I want to have power and exist and a job, fuck you." So, I do not buy it, but since they're a lot better at violence than I am, I refuse to fuck around for fear of finding out. This is one of the many costs of playing the revenge game.
OK, onto actual revenge! The moral calculus of revenge comes down to:
"Is the likelihood of deterrence, and any costs associated with the attempt, worth it to me, accounting for wider society and my position within it."
This is open ended, ill-defined, hard to define, and difficult to calculate. That's just how talking about ethics and morality goes. Tough shit.
You have to worry about the system going after you, you have to worry about what friends the enemy may have, in the system or without, and indeed attracting negative attention from powerful people who are outside the system, but in society with you, you don't like some uppity guy throwing weight around that could become a problem for them.
Let's take some faggot who kicked your dog. If you really are sure you can get away with threatening or attacking him, the issue is then "will this stop future attacks on me or my pets?" and "would this instigate him or his friends into coming after me in turn?"
Let's take, say, Liz Fong Jones. Elliot here has broken the fucking internet, committed all kinds of crimes, and even fucking did so to cover up a prior sex crime. Revenge here can take many forms: staying up despite his attempts to break the internet, censor you, and slander you, fighting back with the system, engaging in "lawfare", or fedposting.
Staying up means you get more attention, but once you're already lost all standing and had to move to Serbia, you've already incurred the cost.
Lawfare requires money, but Null has that now. It might be little more than an annoyance to Elliot, but if it only costs cash Null can raise, and a little time, it's worth it, since he might win. If not, he at least is making a stand and drawing attention to what Elliot is and what he is doing.
Fedposting is retarded. Null does not strike me particularly capable as an assassin, even if he succeeded he'd be an international fugitive and KF would actually go down without a successor arranged before he became Ghost Recon: Slobbermutt, and there's a nonzero risk he'd up thwomped in Elliot's gay tranny sex dungeon, begging for death.
OK, let's take something a bit worse. Somehow, your life is actually destroyed, your future is going to be death in a gutter. Assume you have a crystal ball and know this. Taking the person who did that to you down with you is worth it, for society, because it deters such people from doing this.
This raises the question: should people who are sick or very old "do the needful"? You tell me.
tl;dr -
Don't ignore the risks to yourself
Don't ignore the impact on wider society
Don't ignore the asshole's friends or other big fish seeing you act a fool
Don't waste opportunities by going all in and throwing your own life away
Don't trust the fucking system since it's an amoral instrument of wealthy, powerful people who are currently letting trannies cover up rape and break the internet and facilitating the grooming of children