I think, when you're dealing with a conclusion/elseworlds story such as DKR, then its fine for someone like Batman to kill. But to have him do it on an ongoing basis though, no. Its standard is that he doesn't kill - otherwise what makes him different than a character like Punisher?
Or are you asking this question as if it were a real life kinda situation?

Dear, sweet Harley Kwink...I'm madly in love with you. Marry me! We can go to Canadia. Or Boston or something. It'll be grand...You know the cookies are a given. They are ALWAYS a given. You could dump me tomorrow and you'd still get the cookies. Boston..shit, wherever dyke weddings were legalized. And where better to rub their little piggie noses in how bad they suck than right on their doorstep? What are they gonna do? Be jealous of you? Stare furiously at your tah-tahs? Not willingly give you cookies, but instead begrudgingly give you their cookies? Woman, time to wake up to the powers you wield - Uschi