Some of the best villains are quite sympathetic. Khan had legitimate grievances in Star Trek II. Mrs. Danvers from Rebecca mourned her former boss. Frankenstein’s monster wasn’t the one who initiated the violence. Gollum was driven insane by the ring. Hans Beckert was compelled by powerful impulses. Inspector Javert just wants to catch a fugitive.
There are several examples of this in the Spider-Man comics. Since the most significant villains have appeared in dozens of stories, odds are pretty good that at some point there will be a story which delves into their childhoods, forces them to consider the possibility of retirement, or has them experience a tragedy of some kind. Because of the nature of the medium, the resolution of these stories is going to be the same. The hero is going to fight the bad guy again at some point, so writers have to figure a way to balance the inevitability of that with making the antagonists more three-dimensional.
A Christmas story in Marvel Team Up #1 introduced Sandman’s oblivious elderly mother, and paved a way for his later stint as a hero. The problem was that he had been such an effective member of the rogues gallery that Marvel wanted him to return to that role. So he was brainwashed into being a bad guy by the Wizard, his former Frightful Four teammate. This wasn’t entirely effective since readers are conditioned to expect that type of stuff to eventually be undone. Recent stories revealed him to be slightly insane, as he explicitly stated that he wanted to be a hero but it just didn’t work out. He remains protective of Keema, the daughter of an ex-girlfriend, so he garners some sympathy that way. This also provides opportunities for Spider-Man to temporarily get him to join the side of the good guys if there’s a possible threat to Keema.
There were quite a few stories showing the softer side of the Rhino, partially because he’s so dumb he just doesn’t realize the consequences of his actions. It was played for laughs in Punisher War Journal when he wrote a misspelled letter to offer some comfort to the wife of a cop he accidentally killed. In recent years, the character became darker. He tried to leave the business, fell in love, and then his wife was murdered. After that, he became more vicious and nihilistic, seemingly taking the Silver Sable with him in a murder-suicide.
Another Christmas story by Gerry Conway and Sal Buscema revealed Doctor Octopus’s fondness for Aunt May, an early indication that he had some good qualities. The best Ock story may be “A Small Loss” from Fantastic Four #267, where he was brought over as a specialist to help when Sue Storm got radiation poisoning.Later stories revealed his cruel upbringing. In 2012, he tried to end most life on Earth, so that the descendants of the survivors would remember him, shortly before he vowed to become a hero as the Superior Spider-Man. So his plans have shifted between two extremes.
Then you have the monsters who aren’t responsible for their actions. The Lizard is the classic example of this: a bad guy who really doesn’t have much of a choice in the matter. The main difference between him and the Hulk is that he’s a scientist more often than he’s a green monster in purple pants. However, the Lizards and Morbiuses have the same problem as their stories become less tragic with each subsequent return. Eventually, the reader’s sympathy wears thin, and they start rooting for suicide rather than salvation.
Paul Jenkins took the unusual step of making Curt Connors less sympathetic by revealing that he has always been in control of the Lizard, although this didn’t take. Most recently, Connors decided to punish himself for the death of his young son. Though no one knows where Connors will be at the end of the next Spider-Man VS Lizard TPB.
In a finite work such as a film or a novel, the story can come to some kind of conclusion. In comics, the significant characters will usually return, and the next story is likely to have a different ending. The ending of a villain’s latest appearance usually isn’t as compelling if we know that they’ll be back within two years, and that any crowd-pleasing moments (Electro hugging Spider-Man after realizing his shortcomings, The Kingpin choosing to spare Spider-Man at his wife’s insistence) are going to be reversed.
One of the reasons three-act structure is so appealing is that these stories contain the right amount of reversals of fortune. If things change for the heroes and villains too often, we stop taking their fates seriously. It’s tougher to accept that this particular ending will stick for the characters, and it may just seem like an arbitrary method of ending the latest episode. It’s not as likely to be that perfect ending, where you feel the story couldn’t have ended any other way.
In the DC Universe, Two-Face may just have had the most reversals of fortune. He was a good man who snapped and became a bad guy. But then he’s had quite a few stories in which he regains his marbles, sometimes through the aide of plastic surgeons, and becomes the hero once again. And then he becomes the villain again, as in the first Post-Infinite Crisis Batman arc, in which he took over as Gotham City’s vigilante in Batman’s absence, and killed a few cops when he inevitably snapped. It’s tough to take the character seriously after that, although I did appreciate Scott Snyder’s take on him in “Death and the Family.” The suggestion that he was jealous of the criminals he prosecuted as Harvey Dent is something later writers could play with, and fits the depiction of Harvey Dent from The Long Halloween, the definitive Two-Face origin story. Oddly enough, this is the same thing I detested with the Lizard story, but I like it here.
If a villain is depicted in a sympathetic manner, they’re still likely to commit horrible crimes in their next appearances, which can cause some whiplash for the readers, once again showing that the good side of the bad guy is less effective. One solution may be for the writers and editors to rein these antagonists in, so that readers can still root for them in the future. But that means they’ll be neutered to a degree, if they’re not allowed to be as vicious as the other bad guys.