Adam Dan Din Linafshei/ Vigilantism in Halacha

The Talmud in Bava Kama 27b discusses the concept of Adam Dan Din Linofshei. Translated literally "Can a man adjudicate for Himself" or, as the Talmud explains, does one have to bring his case against his rival to court to adjudicate. The Talmud quotes two Rav Nachman who contends that a man May adjudicate on his own and Rav Yehuda who maintains that one has to go to court and may not take the law into his own hands.

The simple understanding of this legal argument is if Torah law allow for vigilantism. The problem with that is to whom is the Talmud speaking? If somebody takes money out of my pocket do I have to first find out if legally we ultimately follow Rav Nachman's ruling before I know if I can take my money back? Everybody exercises vigilantism to some extent depending on the circumstances and ramifications. If somebody steals somebody's wallet and leaves it openly on a table nearby one will be hardpressed to find anybody that would not take his wallet back! Therefore the problem is from a strictly halachic perspective where is the inflection point where this legal question makes a real difference?

Maimonides rules that one may adjudicate for oneself, below is the text of Maimonides

 יש לאדם לעשות דין לעצמו אם יש בידו כח הואיל וכדת וכהלכה הוא עושה אינו חייב לטרוח ולבוא לבית דין אע"פשלא היה שם הפסד בנכסיו אילו נתאחר ובא לבית דין לפיכך אם קבל עליו בעל דינו והביאו לבית דין ודרשו ומצאו שעשה כהלכה ודין אמת דן לעצמו אין סותרין את דינו

Interestingly, after stating that one may adjudicate for himself, Maimonides adds that "Therefore if the two parties subsequently came to court and it was found that the vigilante acted appropriately the court does not contradict his adjudication" Why does Maimonides add the "Therefore"? that would be a logical extrapolation once we know that we rule that one may adjudicate for himself?

It seems obvious that Maimonides was bothered by the same point discussed earlier. Therefore Maimonides understood that passage in the Talmud not as a question of the allowability of vigilantism (it was obvious that one can  adjudicate for himself if he knows that he is right) but rather as a question for the courts as to its validation from a court perspective. If the vigilante admits to his deed how does the court see that action from a legal perspective is the question. This is not a question that belongs in Pirkei Avos but a question that belongs in Choshen Mishpat