This looks nothing like “brainwashing”. It looks like the standard “peer group pressure” exercise. As Acci commented, it only becomes brainwashing when techniques are further employed to bypass a person’s thinking skills to the point that they “believe” they see what they are told to see. Once that point is reached, it is simply a matter of building up a layer/program of “facts” which naturally lead to a predicted thought process/outcome. (Such as “brainwashing” someone to believe that a certain celebrity are responsible for all of the food poisoning cases involving lettuce in the United States. They are then told that this person must be stopped. Then they are informed that there is no ‘legal’ way to stop them. Then they are handed a gun and 6 bullets, looked in the eye, and told “You know what must be done.”) The person is, effectively, “programmed”.
At each step of the “program”, the task/fact/lesson seems genuinely reasonable. it is when they are all put together that some sense of the surreal takes over.
So it is NOT a case of “Do you believe it”, as you have asked, but rather “Does the assassin/hunter/spy/informant believe it?” (As Accipiter stated.)