Batman's Rogues Gallery has been the goldmine for some of the greatest supervillains in comic book history. Some of them, like the Joker, Scarecrow, and Two-Face, are some of the most twisted and sinister creatures Gotham City has ever known. But then some make the Dark Knight's saga more interesting simply because they don't choose to be villains.
The Batman stories are known for blurring the lines of morality, but many of Arkham Asylum's regular inmates can be easily managed not by Batman beating them back into their cells, but with a sizable donation from his billionaire persona. With the right amount of money, many of these villains would never bother Gotham again.
The Ventriloquist
Arnold Wesker is a man essentially without free will thanks to his wooden personality, Scarface. The psychological horror that is The Ventriloquist is one of the most underrated villains, but he's actually easily defeated quite often. Once Scarface is separated from his puppeteer, Wesker reverts to semi-normal. That's probably why he hasn't appeared in a Batman film yet.
This idea was explored in Batman: The Animated Series, but Wesker still struggled with his darker half. If Wesker was given a friendlier character to express his condition with, he might have gone on to be a happier man. All it would take is for Batman to buy him a different puppet, preferably one with less of a problematic personality. Wesker would probably go on to excel as one of Gotham's premier entertainers.
Humpty Dumpty
Although he received an update in Beware The Batman, Humphry Dumpler is a model inmate in Arkham Asylum. Despite his portly appearance and pleasant demeanor, his compulsion to destroy things and attempt to put them back together is what keeps him confined. That being said, he's much more of a misguided soul than a criminal threat.
He's by no means a bad person, he just needs structure, guidance, and a push in the right direction. Instead of being sent to Arkham, someone should offer him a scholarship to Gotham's nearest vocational school where he could learn how to fix things correctly. This way, the man could not only learn how to mend and bind but become a functioning member of society and maybe even a successful repairman.
Killer Croc
Killer Croc is an evil and monstrous figure in Batman's lore, but despite his reptilian appearance, Croc isn't really the monster he sets himself out to be. He's strong, he's vicious, but he's not a mutated croc-man-hybrid. His form is caused by a skin condition caused by a birth defect that kept progressing until it resulted in his current form.
It might take some serious research, but if a treatment were developed for Croc's skin condition, he might be able to return to a more human-like state. It may or may not affect his position on the Suicide Squad, but that beast-like physique isn't going away any time soon.
The Riddler
The Riddler is one of the most brilliant minds in all of DC comics who has an aptitude for both solving and creating puzzles and games for Batman to overcome, and he doesn't let anyone forget it. With the right direction, his talents could win him a lot more success and acclaim than any of his villainous schemes.
It was touched upon in Batman: The Animated Series episode, "If You're So Smart, Why Aren't You Rich?" but the Riddler seems to enjoy showing off his intellect rather than just causing trouble. In certain comics, he even retired and became a consulting detective working alongside the Caped Crusader. If someone funded and directed his gift, he could easily run his own amusement park if given enough time.
The Penguin
One thing fans forget about the Penguin is that he's not a regular member of Arkham, but a common criminal sent straight to Blackgate Prison, usually for theft, robbery, etc. That is until he starts running the Iceberg Lounge to cover up his unsavory activities, of course. But when Oswald Cobblepot has attempted to rejoin society, he's been shunned and persecuted due to his appearance, even despite his attempts at redemption
It's a subject thoroughly explored in both Tim Burton's Batman Returns and the animated series, but behind his bird-like persona, the Penguin does have a desire to fit in, and he has shown the desire to reform and stay that way. If he put his big scores to finance some needed cosmetic surgery and therapy, he might find it within himself to reform and live out a life running his club as a legitimate business.
Bane
Bane is one of Batman's most dangerous and formidable foes. As the man who broke the bat, the masked, musclebound mercenary has a long history terrorizing Gotham's underworld, even the Dark Knight has had trouble keeping Bane at bay on a few occasions. However, it's easy to forget that Bane isn't just some overconfident thug, but a victim of substance abuse.
Bane gets his power through the use of Venom, a chemical that could essentially be a metaphor for steroids in comic book form. In some comic runs, Bane ultimately succumbs to the consequences of his chemical dependency. The solution is simple, get him into rehab. He doesn't need a padded cell, he needs better treatment. It wouldn't just get him off the streets, it might even save his life. A reformed Bane might be able to walk away from the dark side and live to see the events of Batman Beyond.
Harley Quinn
Harley Quinn has definitely redeemed herself more than a few times, but being Joker's sidekick is more than traumatic. She's been in the clown suit so long that some fans have forgotten that she's a licensed psychologist. And while she has recently found a spot on the right side of justice, her extraneous career doesn't just undo the amount of training and experience she has under her belt. Keep in mind, she does have a doctorate.
Nearly all of Batman's villains could benefit from genuine therapy, but Harley deserves a special mention. With the right treatment and some extra funding, she might be able to help other villains like her turn over a new leaf. She might even be happier at her old job than the Suicide Squad.
Mr. Freeze
There are no villains in all of Batman's comics, movies, or series as tragic or heartbreaking as Mr. Freeze. At no point in his career has he ever done his villainous deeds because he wants to wreak havoc, cause mindless destruction, or benefit his own personal gain. He does his acts of evil in the name of his beloved Nora.
Freeze steals and commits his life to crime to fund the technology that's keeping his wife alive. If someone paid for her treatments and helped him find a cure, he'd no longer be a threat to Gotham. A sizable donation from Wayne Enterprises might just be what he needs. After Nora is saved, Freeze would lay down his arms, serve his time, and spend the rest of his life with his wife.