Are the classes aware of their namespace?
In which case, your security might be broken

AnyPublicClass namespace class allInstances detect: [:e | e name =
#Smalltalk].

Anyway, no need for namespace at all, just a:

(AnyPublicClass withAllSuperclasses last allSubclasses detect: [:e | e
name = #SystemDictionary]) allInstances etc...

Sorry, you might have to restrict available messages too...