Re: If the author wanted a "killing is always wrong" shpiel, he picked the wrong villains.
I dunno about Zsasz but the Joker really can't 'reform' since he's insane; it would require curing his insanity and by that time 'the Joker' as we know him wouldn't exist anyway.
Actually the early last volume JLA has two incidents where the Joker shows that he has something redeemable in him. One issue, they journey into his mind and find this one small part where he's sane. In another, he's actually (temporarily) cured of his insanity and immediately he starts mourning all the people he's killed.
The Joker is the quintessencial character to have for a 'we don't kill' tale simply because at the end of the day the Joker isn't responsible for his own actions. He's insane. What he does is literally not his fault, which is why we have an entire section of law concerned with proving someone is competant to stand trial, capable of understanding the differece between right and wrong, etc.