Whoever fights monsters should see to it that in the process he does not become a monster. And if you gaze long enough into an abyss, the abyss will gaze back into you.
Friedrich Nietzsche said this, and I can't think of a better summary of this kind of RPG play-style. This term (often used as a pejorative, but sometimes meant affectionately) originates from the realization that the core Dungeons and Dragons mechanics primarily supports a play style in which all of the characters are essentially homeless; transients unattached to communities, and have a tendency to resort to solving all challenges by violence and theft.
No judgement here, but if your default play-style is kill first, ask questions never: This is for you.