Hello, new poster but I have lurked for a bit. I'm diving right into this very divisive subject because there is something that caught my attention regarding this conversation when someone posted the transcript of the Fallen Idols episode. I agree with those that think that episode was meant to shift blame and to obscure a lot of what Sam had done in season 4 with the strawman of Dean having been a bossy little brother and I think that it wasn't simply a case of bad writing considering that the same message is repeated toward the end of the season when Sam needs to be let grow up so he can he the hero he was meant to be.
But most of all, that conversation is very very manipulative.
First Sam says that Dean's attitude of wanting to build trust (I do think Dean was punishing Sam by the way which was his prerogative given all that had happened up to that point; petty as it sounds it's human nature) was not how things should go between them because it doesn't work. Then he adds that he feels so guilty nobody will punish him as much as Sam will punish himself (but Dean should stop punishing him because of reasons), which is exteremely manipulative and not apologetic at all. If you have wronged someone, you don't tell them that: you accept their hurt and their way of dealing with it, saying stop punishing me after so little time has passed most of it spent apart is dictating the terms of the relationship. Then he reframes his own actions as being about needing to get away from Dean because he feels like a little kid in Dean's presence and finally he proposes a way to change the relationship that doesn't imply in any way or form any active participation or change in Sam. He tells Dean that (Dean) has to let him grow up. Not I have to grow up, You have to let me grow up. As if Sam has no say in growing up (again the concept of the bossy big brother who is keeping Sam for being the man he was meant to be). Not a single apology for I don't know, lying to Dean, belittling his hell trauma, using it as weapon, or beating him and strangling him when he was already down. The whole thing doesn't end there, by the end of the episode we have Dean apologizing to Sam and accepting blame for the apocalypse and Sam nodding and taking the keys of the car so he "can drive".
In brief, Sam who was the wrongdoer in this situation got to dictate the terms of the relationship by shifting blame onto Dean for his season 4 actions and imposing changes on Dean's behavior and nothing is said about what he will do to make the relationship better. No word about, hey I won't keep secrets anymore, and I won't use your trauma as a way to make myself feel stronger or 'not the little kid to my bossy brother'.
Compare that with the season 9 situation where Sam was the one who had been wronged. In that case too, Sam gets to dictate the terms of the relationship and how it's going to be and gets to be angry for more than half a season. He also says the infamous "Secrets ruin relationships" line which is precious coming from him and definitely not something he has learned given that in season 12 he keeps the secret of having worked with the BMol from Dean. Anyway, yes, it was fair that Sam had a right to be angry but so did Dean in the affermath of season 4, but only one of the two is told to stop and the difference is striking to me in how the two situations are treated.
In conclusion:
season 4: Sam lies, beats, and strangles Dean (and also is responsible for Lucifer getting free, although that is not really the important part as far as the relationship goes), he decides how the relationship needs to change to make it more functional. Dean is told that his rightful anger is an inconvenience for Sam.
season 9: Dean saves Sam's life with a reckless decision, lies to him, and again Sam gets to dictate the terms of the relationship and is allowed to be angry and passive aggressive at Dean until Dean dies in the season finale.
My interpretation etc. but I hope I have sufficiently explained it.