The citizens of Brave New World's futuristic society are in a constant state of imprisonment. But because they've been conditioned to love their servitude, no one seems to have any problem with this. Well, almost no one. As one character so deftly points out, being happy all the time is its own sort of prison; being a human is about having the right to be unhappy. The prison bars are made of brainwashing sayings, of drugs and promiscuity, and not of iron or steel. Because confinement happens in the mind, so too is freedom a mental state.
The hypnopaedic phrase "everyone belongs to everyone else" is the perfect epigraph to Brave New World: no one is free, and every one partakes in subjugating every one else. This phrase goes much further than the merely sexual arena.
John is as much a prisoner of conditioning as are the adults of the civilized world.