These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Being made to kill somebody by a device in your head is awful. Made worse by the fact that the target is your best friend (even if you can't remember that). Finding out afterward that you've had your memory erased SEVERAL times previously and that the only lasting friend you ever had was the man you just strangled to death for reasons you didn't understand... icing on the cake...
The level of suffering inflicted on Malachi throughout the book can be hard to stomach. In addition to being forced to strangle poor Stony Stevenson, he was coerced into joining the Army Of Mars and having an antenna implanted in his head which subjected him to terrible pain whenever one of his superiors decided he'd done something worthy of punishment, decided that he was thinking the wrong thing, or just wanted to torture him For the Evulz. Then, after finally escaping from the army and disabling the agony device, he was trapped in a network of caves on Mercury for three years, being driven temporarily insane by his circumstances. And then, after returning to Earth and getting a great reception as the prophesied "Space Wanderer", it seems things are just beginning to look up for him...but then the proverbial rug is yanked out from under him when Rumfoord tells not only him, but the whole world that he is Malachi Constant, the same Malachi Constant that the new predominant religion on Earth sees as a symbol of everything disgusting and hateful. Rumfoord then springs on him the news that he will never reunite with his best friend Stony, because he killed Stony. (Rumfoord cruelly leaves out the part about him being forced into doing so, thus probably leading everybody on Earth to believe that Malachi was the kind of guy who would happily execute even those closest to him.)