On Killing by Dave Grossman explores the research backing up your friend's assertion in depth. I highly recommend that book to anyone whose interest is piqued by your comment.
Dave Grossman is the guy who goes around giving police departments seminars on the warrior mindset, including telling them that they'll have the best sex of their life immediately after they kill someone in the line of duty.
The core research that "On Killing" was based on (S.L.A. Marshall’s "ratio of fire") was probably fabricated[1]. I'd treat any claims in the book with a lot of skepticism.
> His surviving field notebooks show no signs of statistical compilations that would have been necessary to deduce a ratio as precise as Marshall reported later in "Men Against Fire".
Grossman devotes almost an entire page to the history of controversy over Marshall's results in the Notes of "On Killing"*, p. 336 (Section 1: Killing and the Existence of Resistance") . IOW Grossman clearly acknowledges the debate and welcomes more research.
So out of 400 pages, Grossman only devotes part of one page to the fact that the entire basis of the book is probably fraudulent? That doesn’t seem very reassuring.
Dave Grossman? The fucking Killology guy? The guy who tells cops that the day they kill someone will be the day they have the best sex of their life? That Dave Grossman?