Its not called "neverending battle" for nothing!!! nuff said^^

Batman will never kill and therefore his villains will never stop. On the other hand you'll have to do something pretty bad to stop evil altogether. Look what happened in Watchmen.

Bad Guys go bye bye and the heroes retire. end of story. but evil always seems to rebound, so for every villain you put away, another will following shortly behind. Superman calls it "The Never-Ending Battle" for a good reason.
It's a double edged sword, you can kill 'em without becoming like them etc. I'm sure any heroes who actually think about the fact that the villain they just put away will more than likely be out within the month would probably drive themselves nuts, so it's best not to think on it

I'd say it's the GOOD villains that never go away. Luthor and Joker are classic examples of GOOD villiains, as in those that have strong characters, are related, and fun to watch. Think about how many "villains" we might only see one or twice then never again (or at least until they're reimagined) simply because a "bad guy" does not a villain make.

As long as there a heroes there will be villains. What purpose do heroes have other than defeating the bad guys? No bad guys, no need for heroes. I would like to see some new villains taking over from some of the old guard.

Note to self: Convince heroes to start shooting villains in the face...course that is self defeating because that would make the heroes overly feared and eventually we'd get something like the Justice Lords....Meh :<

It's become cliché now, to have honourable good guys that will never kill... even if though they know the villain will go on to kill again & again.   
 
Then again, for all the times that psychotic murdering villains are caught & incarcerated, they're never given the death sentence :p

When villains are finally stopped that's when you'll see the good writing come out of the woodwork.

that's the beauty of comics though:  the innate representation of duality.  without villains, there wouldn't be heroes & vice-versa...  it's a sensationalized vision of Life in extreme balance...  shutting the villain down would in essence be putting the hero down...  the trials & tribulations are the stones which sharpen the heroic blades...  its a process... dont question the cycle man...  thats not groovy... 

" Batman will never kill and therefore his villains will never stop. On the other hand you'll have to do something pretty bad to stop evil altogether. Look what happened in Watchmen. "

Nope, villains often won't be stopped because heroes are often only half the dynamic of a story.   As Heath Ledger's Joker said to Batman, "Why would I want to kill you?!?! ...you complete me!"   Batman doesn't want to admit it but the reverse is also true.   Villains are the personification of what heroes fight against and the Joker is the ultimate test of Batman's no-kill rule.   Joker defines Batman's refusal to compromise his beliefs, even in extreme circumstances.   In the case of Green Lantern, Sinestro plays a foil to Hal Jordan by presenting an alternative option to creating order and daring to ask why his method isn't just as valid.
 
Marvel is a little different since it tries to play the characters-you-can-relate-to angle.   While some Marvel heroes have foils (Daredevil - Kingpin, Iron Man - Mandarin, Hulk - everyone around him) a lot of them don't seem to have long-lasting opposites.   Some past foils even lose their meaning in their hunt for redemption ( Eddie Brock, Juggernaut).   The reason these redeemed foils fail is because writers fail to give them a new opposite to bring their new direction into focus.   Without a character to contrast themselves against, the redeemed foils become uninteresting and sales crumple.   
 
Why is it that Marvel's heroes seem to do well without consistent foils but its redeemed villains dissipate?   Marvel's heroes do well because they're defined by the events that happen to them.   The X-Men are successful because it's about a group of people dealing with bigotry while attempting to police the extremists in their own ranks that would validate the bigotry.   You don't need a consistent villain for that.   Spiderman has a massive rotating rogues gallery but he's defined by his perserverance in the face of all the personal problems his double life creates.    Captain America's best stories have revolved around asking whether the US still cherishes freedom the way it once did (see storylines where Steve gives up the Captain mantle).   Wolverine is defined by his Kurosawa-samurai approach to life (some may disagree on that).   
 
Thus in the case of Marvel, a hero's foil is not an individual but events that show how a hero faces adversity and his/her villains are easily discarded like candy wrappers.   In the case of DC where the foil is often an individual, the foil will never be truly killed because without him, the strife that the hero confronts would not exist.

Ask Jason Todd what he thinks about it.

" When villains are finally stopped that's when you'll see the good writing come out of the woodwork. "

GOLDEN COD wrote a great response and I agree with it, nicely said.    DEGRAAF also makes a great point regarding how easily the super villains manage to escape wherever they're being detained.   
 
Regarding Lex Luthor, even if he manages to get captured and is incarcerated, he would STILL be able to pull some strings behind bars.  He is that devious and resourceful but I"m tired of Luthor.  Something needs to be done with him.  Kill him off?  I don't know, I have some ideas mind you but I just feel he's way too old hat and while a challenge to Superman, he needs to go or have something totally wild happen.  Simply put, the Joker needs to die.  Enough.  He's been around too long, he's killed too many people, and the fact the DCU heroes have turned a blind eye and/or been too weak to deal with him doesn't make sense to me.  I think other heroes would have stepped in despite Batman's posturing, and done something to Joker by now.    I think DC is just keeping him as a foil to Batman because he's so recognizable.  I think that is antiquated thinking on DC's part.   Batman's acquired new baddies in his rogue's gallery, so having Joker gone is akin to the mythological  hydra; one villain gone, another one appears to replace him.   
 
There are plenty of villains in the Big 2 universes who've not had their moments, and I say let these "2nd tier and 3rd tier" bad guys do some damage for a change, really upset the balance for the heroes.   Do something with the old ones like I said, either incapacitate them, kill them off, what have you, the possibilities are endless.   The stories with them have become old.  DC and Marvel--do something new with the bad guys!! 

No villains no story.
It's really that simple.

The Villains make the Heroes & stores better and without them, their is no comic.

Be nice if they'd actually kill some of these villains. I wonder how many people have died because heroes refuse to kill. You'd think that once they caught some of these people they'd put some mean ass super heroes on guard duty.

The reason that villains (almost) always come back is because they're characters just as good as the heroes.

never!!! villains are what make the hero.

A small number of baddies have turned good or just abandoned crime.  Sandman has stuck to the narrow path for decades now.  Trickster and Pied Piper have flip flopped back and forth a few times.  I can't even count the number of times that Deathstroke has switched sides.
 
The only example I can think of of a criminal abandoning crime and just trying to return to a normal life is Molten Man.  He fought Spiderman and Daredevil a few times, but will now only use his powers on those rare occasions when he needs to protect his family.

In comics the hero, like all the characters, is immortal.  They live on forever and ever.  So their fight with the bad guys will never end because there wont be an end as long as people still want to read them.
Batman was created years and years before I was born, years and years and years and years.  Spider-Man was created during the 60s.  In real time most of the heroes would be old or dead, but in the comics they are still young.  So in Comic Book time not much time has passed, so even though they have faced their enemies too many times to count in their time its only been like 10 years or something.

Can supervillains be stopped? Ask Justice Lords. You can't stop the villains until you start killing them or perform brain surgery on them (by the way, Doc Savage used brain surgery and he is still one of the good guys). "Maximum security" prisons are joke, especially if shady government agencies are offering reduced sentences in exchange fo villains' service.

to quote Morgana McCawber (from Darkwing Duck): "...the bad ones always come back..."

Even if a villain dies, you can bet their legacy draws up something of that same nature for the hero to face. This is the fundimental question: can a world exist without evil?
Without evil, you can bet the majority of the great heroes we know and love would not exist. Therefore, villians themselves have to exist in one form or another forever in order for there to be heroes.
Take the joker for example, Batman and he have faced off so many times. He has died a few times, but he always comes back. Even in the year 1000000 (in DC's One Million arc), he exists in the form of the Laughing Virus
Without a antagonist, who does the Protagonist go up agianst?