Vigilantism is by no means categorically "bad". Sometimes it is the correct, ethically responsible action, such as when an existing system is too corrupt and incapable of delivering justice.
Correctness is subjective, as are ethics. All we have is consensus, and the benefit of exposing ideas to debate.
If you allow individuals to take the law into their own hands, without counsel maybe one time in 100 you'll get an Edward Snowden, the other 99 will be the kind of people who beat up trans kids.
