No one (I hope) disagrees that this is unlawful/immoral. All of these questions assume some kind of enforcement arm of the State. Assuming this exists, then yes--all forms of theft (identity, fraud, etc.) should be liable to retribution (equalling of the scales).

But, assuming no State with a "monopoly on violence," the principle of talionic justice exists prior to any State (a.k.a., Natural Law), so the questuon is really "by what mechanism or institution should retribution be meted out?" How does a given community decide and delegate this power, if we each are not to enforce it ourselves? The "trial by jury of peers" has been the historical way of proving beyond shadow of a doubt (lest injustice obtain) a person's guilt, with the hangman delegated the somewhat unfortunate task of executing whatever punishment the jury-peers (the actual "judges") decide is fair and right.

A society without a sword *of some kind* is a society without justice.

I don't know.

Maybe "the devil we know" (adversarial court system) is better than "the devil we don't" (vigilante-ism)...(?)