I feel like he's still breaking several laws regarding treatment of prisoners of war. If it's anything like our own earth laws regarding that, anyway.

In different and harsh or no, laws are still laws.

EDIT: to clarify, Kat isn't some experts on intergalactic law, but she's gonna react realistically to watching somethoing like that. Yes, Space Pirates are bad and generally destructive, but watching a bunch of people get dropped into a death pit is still pretty fucked.