"Interesting perspective, I won't disagree with you outright. I'd imagine the kid dealt with some bad situations growing up."
Why, because he came from wealth? There is absolutely no evidence to support anything you are saying regarding this person(that he possibly suffered abuse, parents had bad parenting style, were inattentive,I'm sure others I forgot).
In my family, my older brother, well let's just leave it he is the black sheep of the family. My parents were good parents. As far as I know he did not have any "trauma". My parents did both err in that they kept trying to help him and shield him and bailed him out of situations rather than have him suffer the consequences of his actions. But as far as I can tell, the way he is, he was born that way.
I'm sure we are not the only family who has someone like that. If we were a poor family the only difference my brother would be in prison.
I'm not a psychologist, but I am married to one. At the risk of sounding like one of those people that think they gain knowledge by partner osmosis, I'm going to bite on this one.
There's often a lot more going on in a family than the individual members are able to discern. Things like birth order and general disposition differences of children and parents can have an enormous effect on what people eventually become. I don't know your brother or your situation, but I'd imagine there's more at play than just a "bad seed."
When my wife did family therapy the impetus was generally that one member of the family, usually a kid getting in trouble, was the problem. What almost always happened though was after a few sessions everyone stopped turning on the "trouble maker" and started turning on each other. The familial issues were deep seated and a type of Stockholm syndrome begins to exist where you can't really identify the problems in your family. The kid getting in trouble was often the one that was the smartest or most sensitive and most unable to conform to the negative family dynamics.
I'll also say that I was the oldest child in my family and also the "black sheep" if you will. It took me many failed attempts at therapy until I got down to the root of my depression and behavior. I eventually came to embrace the fact that I grew up in an abusive household even though my parents were relatively wealthy, around, and said they loved me. It was liberating to stop blaming myself and start to analyze the issues and find solutions.
When you grow up in a dysfunctional family it's very difficult to break down the cause of your issues without outside help. I think a closer inspection would reveal the source of your brothers behavior.
I am glad that you took responsibility for your own mental health, got outside help if that was needed, and was able to move on. I've known people who were in actual abusive family situations, or experienced real trauma. At some point everyone has to make the switch, from blaming others and seeing oneself as a victim, to realizing one's life is in your own hands and you only have one life. It is up to everyone, to make their life work.
As far as therapy, my brother has been to 2 inpatient treatment centers, an outward bound type camp, and also individual and family therapy, all paid by my parents. He only did what he was forced to, and for family therapy he was often the only one not attending. Our family dynamic is pretty messed up, but it is hard to separate the amount of trauma the rest of the family has experienced because of him, from some pre-existing bad dynamic as you suggest. I would have thought my family was within the range of normal, but who knows? The most significant issue the various therapists had was my mother's enabling and codependency behavior, which would often make the other interventions ineffective. so I do think my mom is kind of messed up because of this relationship she has with my brother, which in turn affects all of us. As far as lack of insight, everyone in our family has had the conversation, with ourselves, with other family members, etc about our family, any way to prevent it from happening, a lot of soul searching in our family (well, except for one). The only pattern I see, the longer you are around this person, the more ruined your life will be. I think the only thing charitable I can say, he hasn't killed anyone yet, that I know of anyway.