God, you guys. Do you realize that Pike's death leaves Kirk absolutely shattered? Broken, bleeding, and floundering in a world that he used to be so sure of. Without Pike there to keep setting him straight, guiding him down the right path, Kirk turns on himself. The dialogue we see between Kirk and Pike at the beginning of the movie transfers to the dilapidated confines of Kirk's grieving mind. You see it every time he's left alone -- when he turns away from McCoy again and again, when he relieves Scotty of his duties and sends him off the ship. There's a glimmer of hope in the shuttle, when Spock thanks him for reinstating his position, but it's gone again as soon as Spock begins questioning Kirk's actions. Kirk shuts him out because he already knows what Spock will say -- he's been saying the same things to himself ever since Admiral Marcus gave them the assignment. He clings stubbornly to his orders, though he would normally fight them, because he knows they're wrong, but he clings to them because he has no idea what to do anymore. Times like these, he would have turned to Pike, but he's gone.
Eventually, Kirk recognizes that. He recognizes how broken he has become, and he confides in Spock that he doesn't trust his own abilities anymore. He turns over command, and it's his first step in the right direction. Going into the warp core is his last. Strange as it sounds, that decision grounds him -- it's the most Kirk-like action he can take. There is no moral question to be grappled with at this point, only a question of value: what do you value most in this scenario -- your crew, or yourself? And of course it's his crew. Of course it's his family. The certainty he has over this decision (it's what Spock would have done, it's what Pike would have done, it's what his father did, and it is what he must do) is the last thread that binds all the shards of Kirk back together again.
