I'm just amazed at the amount of people just completely missing the point of the movie. It is a well-written (and well-acted) exploration into what could be one specific serial killer's upbringing, meant to make people wonder: "is it nature, or is it nurture?"
But then, of course, you immediately get the wise kings among us who make a definite assertion either way. On the one hand, judge, juries, and executioners asserting that, "he was just a bad apple from the start, we need to detect them and deal with them" -- even though, at times, it did seem like he certainly responded to some of the attempts his parents made at reaching out to him. And, on the other hand, we get the perfect parents asserting that, "the parents didn't even try to nurture him!" -- even though, there was certainly something "detached" from his behavior, even at some of his youngest moments we get to see in the movie.
Watch this only if you want to be challenged, but don't expect to be right about your assumptions either way.