Bond is saying that because killing people is routine for him; he’s a wetwork operative for the British government. If he can channel some genuine drive into killing them then all the better. Melina however is not that; eventually the violence she’s doing - even though it’s against people who really deserve it - is going to catch up with her OR she’s going to get killed.These are all starting to blend together but I didn't think she was too different from the lady in Spy Who Loved Me. Because her revenge is unbeknownst to her against Bond she can't complete it but she's shown to constantly one-up Bond. I also think she's played by the better actress/model.
I also didn't like Bond being all sanctimonious and hypocritical about revenge, and pulling a TLoU2 at the end. He murders a helpless Blofeld in the opening to avenge Tracy from SEVERAL movies ago, and then later murders that goon in revenge of the death of the Italian ally (Ferrara) he knew for like a scene. Yet he keeps chastising Melina for wanting to avenge her parents and bullshitting about "digging two graves" for her quest when he's never shown to be conflicted or hindered in his own series of vendettas. And at the very end he prevents her from personally killing the dude, which nearly costs her life.
Or put more succinctly; just because Bond is being a hypocrite doesn’t make him wrong.