*Why* would it be good to have the package statement warn if the symbol table for that package already exists?

Just for grins, I have discerned that the package statement, by itself, appears to cause $::{<package>::} to spring into existence, so that is what you'd be looking for...but I don't see any general value in attempting to make repeated use of 'package X' warnable. In fact, switching the default namespace on the fly is a perfectly valid technique.