"Inhuman," Ctd

You're right that torture cannot be a base instinct, at least on that level. Torture is a complex mechanism, and cannot by itself be encoded into the space between genetic fabric and the environment.  But so many pieces of it are.  The instinct to fight people you feel threatened by.  The instinct to declare and demonstrate yourself the superior.  The instinct to mimic what your compatriot is doing to that inferior person with that watering can and cloth and inclined board. 

What part of torture isn't instinct?  The part where a guy in a chair pens a bloody policy in bloodless language, stating that some level of gore is "acceptable".  That's where it stops being instinct.