Board Thread:False Info and Speculative Discussion/@comment-6383956-20140617174526/@comment-13965604-20140619142327

^ I definitely got that vibe too. But let's not be disappointed when that's not what the writers meant ;P

It's probably some combination of the two. Some are drawn to it because of a traumatic experience and are out for revenge, some are born into families that do it. Hell a few others might just be hunters looking for 'better prey' or guns for hire.