The line, although appropriate, is actually used in The Killing Joke between Batman and the Joker and it is about Joker killing Batman's 'family'. There's always the moral question of what does it take to make a hero into a killer.
I think the reason they use that line on the show is because it IS attached to another daredevil comic canon scene between Frank and Matt where Matt has lost everything, has been outed as DD, is in prison with Fisk awaiting trial, thinks Foggy is dead (in one of THE shittiest choices Foggy ever makes is to let Matt think he's dead and go into witness protection), and Fisk is toying with him daily. There is NO reason to not turn into a killer besides Matt's morals and he's on the verge of giving up. Frank finds out what's happening, essentially gets himself thrown intro prison to help Matt and break him out, and as they're going their separate ways he tells Matt he did it because 'You don't want to be me. You needed to remember that.' I hope we get a similar chat between Frank and Matt this season.
Re: Matt deciding to kill Fisk vs deciding to kill the Punisher
I think the reason they use that line on the show is because it IS attached to another daredevil comic canon scene between Frank and Matt where Matt has lost everything, has been outed as DD, is in prison with Fisk awaiting trial, thinks Foggy is dead (in one of THE shittiest choices Foggy ever makes is to let Matt think he's dead and go into witness protection), and Fisk is toying with him daily. There is NO reason to not turn into a killer besides Matt's morals and he's on the verge of giving up. Frank finds out what's happening, essentially gets himself thrown intro prison to help Matt and break him out, and as they're going their separate ways he tells Matt he did it because 'You don't want to be me. You needed to remember that.' I hope we get a similar chat between Frank and Matt this season.