No one thinks that namespaces are useless and silly. And, of course, Julia already supported methods like Foo.+ that shadow (rather than extend) Base.+, and already supported importing them — that is what namespaces and other local scopes are all about. Your ForceImport package provides some syntactic sugar to import shadowed methods implicitly rather than explicitly, which no doubt is convenient in some cases, but does not change the dispatch or namespace semantics.
The problem comes if you want to extend (not just replace) Base.+, but only in a local context. That is what you initially said you wanted, and that is what the current thread tried to propose also. The difficulty arises because the whole point of extending (not replacing) a method is that one wants to extend the behavior of functions like Base.sum that call + outside the context of your local module. This is what is problematic, represents a complete upheaval of the language if it is even possible (without ending back at something equivalent to the current semantics), and is not provided by ForceImport.