Come on, really? Mikan has killed someone, Chiaki was the traitor, Nagito EXISTS, why the fuck are these children not accustomed to questioning literally everything?

Remember that Chiaki's death left everyone depressed and broken. They were at their limit by that point, they've gone through so much and then they were told that this is all a simulation and everyone can come back to life in the real world. I don't find it that strange for them to accept it as easily as they did, especially when most of them lost a person they hold dear to them to the killing game and desperately want to see them again (e.g. Fuyuhiko and Peko and Chiaki in general).

Also, are we seriously not going to question how convenient that after Chiaki, the Future Foundation traitor, talked to Hajime, he suddenly makes choices helping them? Anyone with two braincells would ask “Why the fuck is Hajime, the one who pushed through with questioning everything, is now not questioning anything?” and that could lead to Hajime hating the Future Foundation for abusing Chiaki like that, not Chiaki because he knows that like how a mouse can’t fly, Chiaki can’t betray the Future Foundation and has accepted that way before the final trial.

There's no reason for Hajime to question Chiaki in that moment, even if she's the traitor and a member of the Future Foundation. It was made plain as day in chapter 5 that her intentions were always to protect her classmates and she literally sacrificed herself with a smile while doing that. She made it clear that she feels proud of herself because she accomplished her objective. Also, Chiaki never pressured Hajime into choosing either of the two choices he was presented with, she told him to stop thinking that he's limited to only those and create his own, because unlike her he's not part of the game.

Also, just a sidenote, there might be an argument to be made about Chiaki being the more helpful of the two, but Nagito quite literally saved everyone's lives in class trials more than anyone. For example, he's the one who drew attention to the burn marks on the rope, which exposed Mikan's lie about Ibuki's cause of death. He always leads everyone to the right answer in many instances. He doesn't just happen to know everything and keep it to himself except for the stuff he found out in the final dead room. I don't want to make too many assumptions, but you should probably try looking past your hate a bit to understand Nagito's character more.