Guns are only weapon you need in modern RPG setting?

[The Glyphstone]

But aren't their studies that show humans can be remarkably blase with their response to hearing screams?

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Civilians, maybe, and even that is heavily dependent on the local area. If you're just out randomly murderizing late-night joggers, silence is less important than your ability to escape the scene of the crime quickly. If you're concerned with being quiet, you plan to stick around, which probably means you're somewhere with security guards or other significantly more alert and scream-sensitive people.