First, a little bit of history for those who are young, disinterested or foreign: in the 1988 Presidential Election, Michael Dukakis, the democratic Presidential candidate, was asked during a presidential debate, whether he would favor the death penalty if his wife was raped and murdered. It may be debated whether that is a fair question to ask in a political debate, but leaving aside the issue of fairness, it is usually agreed that Dukakis' answer didn't do his campaign any good. He responded flatly and unemotionally, explaining that he opposed the death penalty and always would. It was one of several moments that cost him the campaign.
And now, for an explanation for those of you who aren't comic book fans, it should also be explained that most mainstream comic book characters also have a code against killing. I don't know if this is a remnant of the Comics Code Authority, or whether publishers just want to be, or appear, socially responsible. Other than with anti-heroes such as the Punisher, or in titles from smaller companies, super heroes usually go out of their way to avoid harming even the most despicable villains. And as a further point in comic book history, around about the late 1980s, comic books were often darker, with murderous, angry super heroes taking market share away from the upright, American Way adventures of Spider-Man and Superman. And comic book writers and editors could have addressed this in many ways, but instead they did so by having super heroes get into moral dilemmas about their code of ethics, which was always followed by the super hero giving a soliloquies to the extent that "It's not for me to decide!" or "If I stoop down to his level, I will be just as bad as he is." Which would be good if these are presented as great ethical revelations, but just as with Michael Dukakis' speech, they always seem scripted and stilted, especially when the supervillian in question has actually harmed an innocent person, including someone close to the superhero. I could give many examples of this, if I were to search through my gigantic collection of 1980s comics, but I am assuming that those familiar with the period can think of a few examples for themselves. And it was presented as a theme not only by the typical medium grade comics, but even by such masters as Alan Moore, (although of course Moore does it with more finesse). In The Killing Joke, Commissioner Gordon insists that Batman bring in The Joker "By the Book", even after The Joker has shot and paralyzed his daughter.
I don't know why it was such an important point to make so frequently, especially since, unlike Michael Dukakis, super heroes, and the writers and editors that controlled them, weren't under any specific compulsion to deal with weighty issues. If they were going to deal with these issues in an interesting and enlightening way, that would be fine. However, if they must resort to boring, cliched dialog to do so, then they should have just decided to go back to stories where Spider-Man playfully wisecracks his way through disrupting a jewelery heist.