We've had various versions of the Joker so Batman not killing him to uphold his 'no killing stance' would make sense when it was a 'one off' appearance by that villain in regards to the movies or maybe even the animated tv series I have yet to see in full. However, the comics really show him to be a menace and someone who seems to continually get off easy w/o Batman really influencing anything...even the police or Arkham Asylum who continually takes in Joker and he continually escapes. And, even gets a crazy companion named Harley Quinn....![]()
It sounds just like the real-life justice system in some countries.

The number of times I see people in my local papers who are as guilty as molasses of whatever crime, and are even given a guilty verdict by a jury, but then promptly get given a suspended sentence and are let free by the judge..... it's crazy.

Bats knows this, and respects the justice system, even though he knows first-hand how flawed it really is. That's why he's always there to put the Joker away again every time he gets out.
I guess the discussion is really about rehabilitation. Gotham's justice system evidently works on a level similar to some justice systems we see in Western societies: the bad-guys aren't just 'locked up', they are 'rehabilitated' to become members of society again. The criminals know this is how it works, and exploit it. Batman's job isn't to stop crims, it's to deliver them to justice so justice can do it's job. Even though, inevitably, he only ends up having to do so again when somebody like the Joker gets released and promptly becomes a psycho again.