Some time ago a computer scientist named Matt Blaze wrote a rather informative article on some rather serious flaws in common masterkeying systems. Specificaly the flaw described by Blaze enables a relatively unskilled person to make a masterkey for the system in question based on nothing more than unrestricted access to one lock in the system. e.g. a tenant in an apartment complex making a master key for the complex from nothing more than the master keyed lock on his own door and posession of hie own key.
The Matt Blaze paper can be found linked to here:
Why are these masterkey systems not only still in use but more of them being implemented every day when they are fatally flawed? Do you not have an ethical obligation to your customers? Why should you not be liable in civil court when systems you install which are known to be insecure are compromised?