Killing is not so easy as the innocent believe.

The line suggests that taking a life is not merely a physical act but a moral, psychological, and practical threshold that most “innocent” people underestimate. It implies that those unacquainted with violence imagine killing as straightforward—an on/off decision—while in reality it involves fear, hesitation, consequences, and often a lasting alteration of the killer. In a Rowling-associated context, the sentiment would also resonate with the idea that murder damages the perpetrator (ethically and spiritually) as much as it harms the victim, and that innocence can be a kind of naiveté about what violence demands of a person.