The incredibly sad case of Jaxson Jacoe is a recent and excellent example of why vigilantism ultimately fails as a means to serve justice. This 21-year-old, Burnaby resident with developmental disabilities was recently ambushed by a few guys from the Langley Creep Busters and White Rock Creep Catchers networks, vigilante organizations that hunt for pedophiles online, setup fake meetings, then confront their targets, usually with cameras in hand. Such organizations have become popular across Canada and other countries recently. Much good work has seemingly been done by some of the groups, as they often provide information to the local police that assist in laying actual charges and, presumably, obtaining convictions.
But these groups have also needlessly, and wrongly, destroyed lives. Jacoe was confronted by the vigilantes at his work and promptly lost his job as scorekeeper at the Planet Ice arena in Coquitlam. If you read the CBC report linked above, you'll see that Jacoe's disabilities rendered him incapable of dealing with the confrontational situation, and he will likely deal with lasting trauma from the incident for years to come. Most importantly, there is zero evidence that Jacoe is a pedophile by any reasonable definition of the term. His social faculties are on par with those of a pre-teen, and just because he agreed to meet an allegedly 14-year-old girl because "she" was interested in becoming friends, does not a pedophile make.
The whole situation is an example of Type II error, or "false negative", in action. Much of scientific methodology is traditionally concerned with controlling the rate of Type I error (the rate of "false positives") first and foremost , and then designing studies or adapting analytical tools to minimize the rate of Type II error, in some sense. (Yes, the reality is a bit more complicated than this, but the general idea works for this discussion.) To take a specific example, it is far preferable to mistakenly infer that a drug does no good (false negative) than to mistakenly infer that it does (false positive). Patients consuming a drug that does no good are not actually being treated (minus any placebo effect), and in the meantime many of them could be getting worse. [Interestingly, there are plenty of instances when we actually care more about controlling the rate of false negatives, but that is probably best left as a topic for another post.]
The Canadian justice system, and those of most other secular democracies/republics, operates under the same principle. This is the classic "innocent until proven guilty" credo reformulated in statistical terms. As Blackstone's formulation asserts, "It is better that ten guilty persons escape than that one innocent suffer." Put another way, it is better that we commit a Type II error (incorrectly infer someone is innocent) than a Type I error (proclaim an innocent person guilty). The default, or null, position is of no effect; in this case, that means no guilt. It should require ample evidence to move us from this null position.
As a natural consequence, our justice system allows some guilty people to roam free (a Type II error), those for whom enough evidence is not available to ensure a proclamation of guilt is not simply a Type I error. Of course, no reasonable system of justice carries with it a zero chance of Type I error (otherwise, no one would ever be declared guilty no matter how much evidence was stacked against them!), but it seems eminently preferable to live in a society where you don't have to be worried about convincing the state that you are innocent should they decide to correlate your location or habits with the occurrence of a crime. You found someone's wallet on the bus and want to return it? Too bad you have to prove you didn't really steal it first. This is not a system of justice that one would like to live under.
This is the system of justice enforced under vigilantism, however. Though often well-meaning, vigilantes like the Langley Creep Busters and White Rock Creep Catchers trade Type II errors for Type I errors. They subscribe to the theory that it is better to catch all criminals at the expense of snaring some innocents, and eschew Blackstone's formulation. When they confronted Jaxson Jacoe outside his work on February 20th, they did so with a verdict already rendered. He was guilty in their eyes and now justice had come to be served. Of course, they were wrong in this instance (a Type I error), and the consequence is that they have destroyed this young man's life, a life that will be very difficult to put back together given his developmental disabilities.
The allure of The Batman is undeniably strong, on a visceral level. If I happened to be The Joker's dry-cleaner though, I would rather not have to deal with Batman beating me up under suspicion of laundering money.
[P.S. It is true that our classical justice system also commits Type I errors, but there are many mechanisms in place to minimize the chances (burden of proof), and to correct such mistakes after the fact (the entire system of appeals). Incidentally, this is a good argument as to why the "death penalty" has no place in a modern judicial system. Putting a convicted person to death eliminates any future possibility of appeal, or the relevancy of new evidence, and thus ensures that some Type I errors will never be rectified.]