What does Helmholtz find absurd about John's reading of Romeo and Juliet in Brave New World?

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.