I'd need to read those arguments before rebutting them, but for clarity's sake, I doubt whether piety or secularism (or atheism if you insist) has ever been the primary impetus for violence. Greed - for power, money and sex etc., as well as fear and shame are probably always at the center of such tragedies, and ignorance probably explains the rest.
Even horrors typically attributed to religion - the Inquisition among them, surely arose directly from greed, lust, fear and misogyny - not religious faith.
But faith can be an unbelievably powerful weapon (even unintentionally), and as far as I can imagine, in ways that secularism/atheism cannot.
TL;DR
Faith isn't the cause, it's the sword.
Secularism/atheism isn't a cause, nor much of a sword. Maybe it'll be considered a pen eventually, but these metaphors are quickly becoming an unwieldy mess.