If the slave were interpreted as a composite body, it would also mean
the entire group of faithful slaves turning evil in order to become "that
evil slave."
Such a scenario would leave God's household at the mercy of wicked
slaves with no one faithful to care for the belonging. However interpreting
the slaves as individuals precludes such an event.
An individual slave could become wicked but, other faithful slaves would
be on hand to feed the domestics.