The subordinate clause <em>who can carry a tune </em>is used as an <u>adjective clause, </u><u />because it modifies the subject, which is the noun people.
What kind of people? (Those) who can carry a tune.
Based on the question given this is the answer:
The punishment was justified because it was simple and
straight to the point for the baby’s name to be mention early. It reflected the
characters actions and if there was any punishment that was even crueler that
wouldn’t be very fair.