Does this example help: There is a name defined in Base, e.g. `pop`. In languages that do not use multumethods, when you created your own "FancyContainerLibrary" you need to create a new `pop` and ensure it does not clash with `Base.pop`. In languages with multimethods you just extend `Base.pop` to work on your new type. Julia can do both: it has perfectly normal support for namespaces, but frequently you will be extending Base methods instead of working in your own namespace (of course, all your private functions are usually unexported and available only from your namespace and do not polute the global space).
You know, maybe you're right and I can't prove you wrong, but this is the kind of thing that IMHO application developers read and think "yeah no, been there, done that, never again". Because many people's experience is that names do clash, again, and again, and again, and I fail to see why multimethods should solve that.