Народные защитники

08:51 Jun 15, 2016 

There was no eagerness on my part whatsoever, just a natural and quite justifiable (if I may) desire to seek clarity, okay? :-)
I am afraid I'll have to reiterate: I didn't borrow 'what I've offered as a translation' (it's very nice of you to put it that way) from a dictionary. I was perfectly aware of what 'vigilante' stands for, but I had to look it up after you began to 'question' 'what I've offered as a translation'. That's how I came across the definition and ultimately found out that there is, in fact, nothing tautological about 'self-appointed vigilantes', which was later kindly confirmed by the native speaker Rachel Douglas (just in case it escaped your notice).
Also, I can't for the life of me see how could the 'Russian idioms'(??) "Ты чего в защитники лезешь," Ишь, защитни(че)к выискался", possibly support your point here. And finally, my approving Mark's answer doesn't make my answer a tautology, I approved it because I thought it was better than mine.
To sum it all up: considering that you haven't been able to come up with any solid arguments in support of your claim, I really don't see now why would I start this discussion in the first place! :-) All the best to u 2.

00:35 Jun 15, 2016 

The eagerness with which you insist to "get this straight", implies a sort of... emergency. I hope I'm not too late.
Why on earth should we bother about someone borrowing something from a dictionary? It is what dictionaries are for, anyway :) But here's at least two important reasons to question what you've offered as a translation.
1. A vigilante is always self-appointed, otherwise he wouldn't be a vigilante. It is not a dictionary definition, but historical fact. If we look for a biological analogy, vigilantes are "antibodies" produced by society; it is a defense mechanism against something harmful. Linguistically, my point is supported by Russian idioms "Ты чего в защитники лезешь," Ишь, защитни(че)к выискался", etc. Ergo, "self-appointed vigilante" = "масло масляное".
2. A person of the street would never use this wordy, book-learned I'd almost say, expression. Unless he is a professor of medieval studies.
Lastly, Mark has offered a perfect translation which you approved, by the way.
Summing up, I really don't see why we should spread this discussion beyond its current scope.
All the best.

17:46 Jun 14, 2016 

@Some writings are only good as an example sentence in the dictionary@
As long as you realize that I didn't borrow/steal my answer from the dictionary :-)
Let's get this straight, shall we? When you wrote 'self-appointed is a tautology' I assumed that you were simply referring to the definition of the term, which reads as follows: 'A member of a SELF-APPOINTED group of citizens who undertake law enforcement in their community without legal authority'. Therefore 'self-appointed vigilante' might have indeed sounded somewhat tautological to you. Now, since you weren't referring to the definition, you obviously must have had some other reason behind you claim. Would you kindly share it with me? What exactly makes 'self-appointed' a tautology to you? Thank you.