While he still feels guilty over his father's death, the sheer rage over easily it could have been all been prevented is all consuming.
If Krillin had used the detonator then Cell would have never been able to become perfect. Cell would have been stuck in his semi-perfect state and would have been destroyed by Vegeta, Trunks, his father, or even himself.
If Vegeta had decided against allowing Cell to absorb 18 then everything would have been prevented. Vegeta could have been the hero that killed Cell, his father would be alive and Goten would have his mother, brother, and father to watch him grow.
If the all consuming power hadn't overwhelmed him then he wouldn't have let Cell suffer. He would have killed the monster brutality and coldly. Not for the sake of enjoying it but to make the monster feel the terror he inflicted upon others before he was destroyed. If the power was controlled than his father would be alive, his mother wouldn't cry, and he wouldn't have nightmares.
If his father decided to actually train him in using the overwhelming power, instead of relying on blind faith than things would have been so much easier. After all if his father actually tried to him help unlock it and control the new transformation than the power wouldn't have overwhelmed him so. His father, who surely stayed away after Namek to control the Super Saiyan transformation, should have realized that an even higher level than Super Saiyan would be even more difficult to control and would overwhelm without proper guidance.
The rage is all consuming and it is being fuelled by constant what-if thoughts in Gohan's head and he knows that he has to stop the fire before it becomes an inferno. So he laughs and goes day by day, reminding himself of all the good and aid that Krillin, Vegeta, his father, and himself have provided.
He's remarkably adjusted after his father decides to stay dead, because he wants the inferno raging through his body to evaporate.
Author's Note: No one is meant to be bashed but the one-shot works better without a comparison of the good and bad. Not going to lie I feel that more could be with it, but I'm unable to think of something, despite this I am posting this because I feel that the flow of it all works.