If both Mother and Father have DESTROY methods, what happens?
Under normal Perl semantics, only Mother::DESTROY would be called, since it's the left-most, depth-first method encountered during the dispatch.
But failing to call one (or more) of an object's inherited destructors is not correct behaviour. Hence the need to be able to call all of them:

The problem this solves is very real-world. Consider a Perl class hierarchy in which a class Child inherits from classes Mother and Father:

Uh, oh. Multiple Inheritance.

A couple of years of doing Smalltalk (which didn't have multiple inheritance, but which let you fake interface interitance via mixins), and a couple of years of Java and C++ have lead me to believe that Multiple Inheritance is a Very Risky Thing, and that it can always be worked around by either composition or reducing to inheriting from one data-bearing class and multiple (data-less) interface classes. Doing so avoids the multiple destructor problem.

Perhaps you've run into a situation where multiple inheritance is the right thing to do. If so, I'd like to hear about it.

It happens often in LPC. It's a language mostly used for
building MUDs. Often you will have a standard weapon
class and a standard wearable class. All weapons inherit
from the weapon class, while all wearables inherit from
the wearable class. But boxing gloves would inherit from
both.

Some problems LPC has with multiple inheritance aren't found
in Perl (for instance, the possibility of duplicating variables
when a class is inherited by two paths - different implementations
of LPC solve it differently). Other things are solved differently,
for instance, one flavour of LPC forbids inheriting from two
classes if they have methods with the same name - unless the
inheriting class defines a method with that same name.

There is nothing wrong with multiple inheritance. It's just
hard to implement is right, which is way some languages take
the easy way out and outright forbid it. Inheritance is already
a hard problem in Perl, but multiple inheritance is a real
nightmare. But that's the fault of Perl, not of multiple
inheritance.