What's "justice"? Outing the plagiarizers does nothing to get them to do the right thing in the future, their ability to contribute is virtually eliminated. This hurts the community if this is a one-off event but they otherwise have made or can make useful contributions. If this is habitual, then outing them improves the community (as they're a net-negative to the community).
So reasons to out: habitual behavior that's a negative to the community; to make the injured party feel better (in some fashion). We've already addressed habitual behavior, outing is appropriate as they're a net-negative. So the second needs to be address, satisfaction for the injured party.
The publication is out there, what the true author wanted, and people can base new work on that (by way of citations and reading it). So the only thing for the injured party to gain is satisfaction at knowing the offenders are hurt and that they (true author) will get credit. But this is vanity, and other than the potential for that credit to provide the true other with greater resources (due to proper recognition in the future for their, potentially, valuable work), there is no benefit to the community. And if the true author's work is of value, and their work isn't frequently plagiarized, then their personal career is going to be fine.
Exceptions, of course, are important to note. I knew someone in grad school who had a professor plagiarize their work (and not their advisor, either). This greatly hurt the grad student, as this was one of their early publications (first significant one, maybe?). It also greatly hurt the plagiarizer who lost a lot of standing within the department (I don't recall what all became of either of them, I was on my way out at the time). We can always construct ever more exceptional cases that show that extreme (by some measure) responses are justifiable in the name of justice. But moderate responses are certainly also worthy of consideration, and probably ought to be considered more often.