That's pretty much the situation we find ourselves in with these "real-life superheroes." While they certainly have enough cajones(even the females) and good will to try to bring down criminals, at the same time, they're putting the general population at risk whenever they pick a fight with these guys.
To be fair, when the police attempt to take down a criminal, they are also putting the general population at risk. The difference comes in terms of training; ideally, the police have been trained to minimize the risks involved.
However, there seems to be a difference in situations; the bank robbery occurred around a number of other people, the entity being harmed could easily endure the harm being done to it, and the police would have been involved regardless of the teller's actions. But imagine a different setting; it is night and there is a woman being pulled down an alleyway. Almost no one is around to notice, and almost no one has even an inkling of doing something. That "almost on-one" being a "superhero" out on patrol. Certainly, by interfering the individual would be putting the woman's life in danger, but it is unlikely there would be many others caught in the crossfire. The victim may or may not survive the harm that is plotted against her, and police involvement is not a sure thing. Now, the superhero could call the police, but the likelihood of a timely response is rather low (at least, until there are gunshots).
In the case of the teller, the potential for harm from interfering was high when compared to the harm being done. In this case of the superhero, the potential for harm from interfering was comparatively low to the harm that might have been perpetrated.
Of course, I couldn't tell you how often these superheroes do good and how often they cause harm. To my knowledge there aren't many studies done on the matter.
But there's another, much more sinister side to this: vigilantism, and that is nothing to support or be proud of.
Maybe. Vigilantism is often given an overtone of revenge, in the public eye. A movie might have a child kidnapped and then the parents taking the law into their own hands, hunting down the kidnappers and killing them. That is vigilantism, and I can understand how one might not support that. However, let us say that you are at Disneyland and all of a sudden a little girl starts screaming that the man dragging her along is not her father. Surely, you should do more than merely stand there and maybe call the police. By stopping the man you would be taking on the role of a law enforcer, thus stepping into the realm of the vigilante. And yet, I would argue that if you did not do so you would actually be breaking the social contract. A society cares for its members, and while we have ordained specific individuals to take on that duty for society, that does not free us as members of society from still being aware of those duties and fulfilling them when there is need.
Vigilantism is problematic when it is taken to an extreme, when the public and the law suffer because of it. However, society and the law suffers when the citizenry ignore their duties to society, they suffer when the citizenry ignores need merely because that isn't their responsibility. Yes, society has established representatives, it has established workhouses and prisons. But to say that these free the common individual from actively caring for their fellow humans is intolerable; it is akin to saying that if people cannot go to these established social institutions, these workhouses and prisons, for help, or if they would rather not go, then that they should die and decrease the surplus population.
To cross the line from being vigilant and caring to being a vigilante might be a dangerous thing to do, but to approach that line, to be as caring and vigilant as possible, is good. To be great one must risk great consequences. Sire, those consequences can be bad, but right now, society rarely thinks about making the attempt to greatness. Let us worry about going too far when we start going at all.
Plus, wherever there are "real-life superheroes," there must be some real-life super villains, and I can only imagine what they would concoct.
The thing is, there world is already full of would-be Lex Luthers and Dr. Dooms. We have the villains, and we the common citizenry have the power to stop them. But our reaction tends to be that with great power comes great delegation. A little awareness, a little concern for the welfare of others, a little action, and the world would be a goof step closer to a utopia.