The interesting key feature of this chapter is that O’Brien recruited Winston. O’Brien gave him Goldstein’s book and told him of this ‘Brotherhood’.
Before O’Brien’s intervention, Winston had no idea such existed nor was actively pursuing some kind of ‘anti-Big Brother’ movement.
Nothing Winston did effected anyone else or any aspect of society. So why waste time and effort to arrest and torture someone for ‘thought crime?’
The crucial take away is the the 2 + 2 = 5. This is where a human mind can be so controlled as to see what one is told to see.
For example; the fact that supporters of Donald Trump can see a photograph comparing the crowd at his inauguration to that of Barack Obama, and because Trump says he had 3x more people, actually believe it, despite the evidence.
That Trump can dismiss the Corona Virus one day as a hoax, then recommend chloroquine, which can kill after two dosages, without wide spread confrontation is clear evidence that the kind of mind manipulation described in Nineteen Eighty Four does exist, and does work as desired.