This scene, occurring in Chapter Twelve of this tremendous dystopian classic, reveals a lot about the kind of morals and values, particularly regarding sex and relationships, of this new society and how even the more enlightened of its members, such as Helmholtz, are impacted by these sexual mores. We are told that as John reads this play to Helmholtz, everything goes well until the part when Juliet cries out against the way in which her parents are forcing her to marry Paris when she is already married to Romeo. Note Helmholtz's response:
The mother and father (grotesque obscenity) forcing the daughter to have someone she didn't want! And the idiotic girl not saying that she was having smeone else whome (for the moment, at any rate) she preferred! In its smutty absurdity the situtation was irresistibly comical.
This is why Helmholtz "laughed and laughed" so dramatically, as he only is able to understand the situation facing Juliet through his own cultural lenses based on a culture where sex with as many people as possible is encouraged and any notion of loyalty or fidelity is so bizarre as to be considered a sickness.