besleybean wrote:

That was kind of my thinking...it's  not like John  had never heard of a fake death and Sherlock told him it was a magic trick...

He might have believed at the beginning. But after two years? 

If you have seen a person jumping from a building and after that you see it coverd in blood on the pavment, how much hope you have that is a fake dead? One cannot compare with Irene's dead, where noone was there witness with Sherlock's dead, where John believed to be the witness. 

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(I don't know if i should put my answer in the new thread or in this one, if not welcomed, i can remove it).

I read and read here how John cannot keep his anger under control. Actually he does a lot and has only few times where he is not keeping it togheter. 
- cabbie death - here is not John not keeping his anger, anger has nothing to do with it. He is a soldier, trained to take quick decisions in dangerous situations, he took it. He is at peace with it, for him was a perfect moral decision, can go eating after that.
- punching Sherlock in ASIB: he got over the board after Sherlock's punch, but he might have intented as a lesson. For me the meaning was: do not provoke me, i am keeping myself hardly under control, so it looks when i don't, it is not a joke for me. 
- punching the chief intendant : for him kind of moral decision to fight for Sherlock and what he thinks is the truth, naturally he should have not did it
- punching Sherlock in TEH: actually without thinking, Sherlock blocks John's attempts to deal with the whole bunch of shock,anger and emotions. John's tries to explain his feelings, he is on a verge of nervous breakdown and crying when Sherlock comes with the stupid nervous joke - typical missunderstanding. The third time John tries to get off his anger by shouting, Sherlock shush him - kind of bad idea, he would have cooled off .  We see that at their next meeting, John is still sour, but he had time to cool off, he is now prepared to deal with it, the shock is gone.
- spraing the arm of Billy: he was showed a knife, he feels under threat, he reacts. But his violence here is not at all without control, he goes only as necesarry till he got the knife. 
- throwing/pushing the chair at 221B: he did it and after that he controlled himself (with great effort and with the help of Sherlock, but he did it). 

We tend to forget, because he seems and mostly behaves so normal, that John deals with PTDS. So actually for someone dealing with PTDS, where anger is a big issue ( http://ptsd.about.com/od/ptsdandthemilitary/a/Iraq_anger.htm ), he controls himself rather well. Yes, he has issues with anger, he needs to control it, we see it bubbling under his skin some times, but he is not such under losing it. There are many times when Sherlock makes stupid jokes, when he lies John, when he put John under stress situations (lab in HOB anyone?), when John can control his anger very well. He even controls himself under the humiliation of CAM.  

We might look at Sherlock to compare a bit and put it into perspective. Sherlock gets mad at the cabbie and put his foot on the wounded part (on a dying man). Throwing of the agent through the window in ASIB was unnecesary, he had the situation already under control. He kills an unarmed person (yes, a very despicable one, but still unarmed). He normally controls his anger much better than John does, but he has his own demons to fight. 

So i don't see John as a violent and uncontrollable person, but a person who struggles with a lot of problems. That the most violent episodes from John's part happens with the beginning of TRF, is also telling a lot .  Dealing with PTDS is not easy alone, dealing with additional problems like losing a friend, seeing him die, being betrayed by your friend and by your wife might turn you upsidedown and make it harder. I think we might see him learning to deal with his problems in S4, as we have seen Sherlock dealing with lots of his in S3 - for example from John's anger and pain he learns a lot about friendship, he sees the consequences of his acting in a new light. 

Neither John and Sherlock are totally white. They are 3D-persons with good and bad fighting inside, sometimes doing the right thing, sometimes doing the bad things, trying hard, getting wrong. Human nature. Not only they learn something about life, we might learn something too. That someone is violent is not an invitation to be one (and we see actually in this series very little from it in comparation with normal TV). But a lot of people are violent and there is a reason most of the time behind it, we will not learn to deal with it by shuning the phenomen.  And how boring would have been to have an i-do-noting-wrong Sherlock and John?
 

I somehow missed your post, A Lovely Light.  Thank you for the breakdown of their violence.  I agree that they aren't angels.  It's flagged up right in the first episode that both are attracted to the darker side, to excitement and danger.   It's what bonds them.  I'm not even sure that John has PTSD (Mycroft doesn't think he does).