Kira said: "sure you can" what Dues saw was that when kira was 3 when his parents failed one too much mission and the boss in person came to kill them, then he took kira to raise him as an assassin, but he turned to be more of a spy, and kira swore to himself he would have killed him the 1st chance he got.
the training for him wasn't harsh at all, he had a fast mind and learned fast, so the teachers didn't need to punish him, he quickly learned how to behave too, he liked to spy on people, and absolutely hated killing people unless necessary, and performed very poorly in assassination tasks, of course he absolutely hated everybody else, most of the people who worked in the "company" were assassins, or generally deviant people who liked to cause suffering, kill or spy, so he really spent as little time as possible with them and as a result everybody hated him too, and were just waiting for a chance to have their way with him (this is in his mind so, some things might be twisted or overthinked, or even wrong)