People are who they are because of combinations of genetics, memories, material experiences, and everything related to them. For example: peer pressure, people want their peers to accept them, as with animals - those who don't 'fit' will be removed from the 'herd' - so they do things they think their peers will like. Using myself to show this: when I read a blog, or comic, or thread on the internet, sometimes I'll write a comment - such as now-, but often I will look at that comment, and believing that it will upset my online 'peers' and that they will (remove me from the herd) ban me from the forum, I decide not to leave the comment.
Anyways; Who we are is shaped by our lives, sometimes this isn't the best person we could be. like the boys in the article. sometimes people grow lacking certain morals, or the ability to control natural impulses and instincts that need to be controlled.
...and some people have genetic combinations that just shouldn't be allowed to reproduce.