Batman has one of the most iconic and dangerous rogues galleries not just in the DC Universe but in all of comic books. However, while these villains are undeniably harmful, they might also be providing the Dark Knight with a layer of protection that he otherwise wouldn't have.
Gotham City is home to some of the most demented criminals in the entire DC Universe. There's a reason why crime has only been decreasing slowly despite the fact the Bat-Family is almost in the double digits with members. It's difficult to reduce crime in a city that houses Joker, Mr. Zasz, Professor Pyg, and Deacon Blackfire. This could lead people to think that Batman's rogues' gallery is entirely evil or have no benefits whatsoever, but this isn't entirely true. Even recently, DC has admitted Joker can be saved so while his villains are some of the most vicious in all comics, they aren't pure evil. Additionally, they do have one unexpected bonus which is that most of them want Batman to keep living.
The unexpected benefit of Batman's villains was revealed in Todd McFarlane and Greg Capullo's Batman/Spawn #1 which saw Spawn needing to go after Batman for something, but Spawn admits getting close to The Dark Knight won't be easy due to the colorful villains that surround him. Spawn explicitly states "They wanted no one near him but themselves" which is true for most of Batman's villains. Joker, for example, has made it perfectly clear why he and Batman will never stop fighting. But other villains have also expressed obsession and an unwillingness to share Batman with others, for example, both Bane and Riddler only really hang around Gotham City to try and best The Dark Knight, and both villains have also helped Batman at different points in his career.
Batman Is Guarded By His Villains
While there's no doubt that Batman would prefer crime to simply stop and for Gotham City to be a safe place for all, there's equally no doubt that a lot of Batman's villains are specifically obsessed with him and gaining his attention. This is most obvious with the Joker, who quite literally bases his entire existence around his relationship with Batman, and other villains have done the same. For example, Scarecrow has never really expressed any interest outside of Gotham or his battle with Batman. While some of Batman's villains are multiversal-level threats, others are just serial killers that want nothing more than for Batman to come after them, and they're willing to fight anyone who threatens to take that away from them. While it may not be the best benefit, it's still a benefit Batman has nonetheless.
Batman's villains aren't single-mindedly evil and while they do unbelievable harm to the citizens of Gotham, they also inadvertently protect the man who is doing the best for Gotham City, especially considering the fact that there are other villains in the DC Universe such as Lex Luthor who'd undeniably be glad to be rid of Batman once and for all.