I skimmed through it but couldn't really understand why they couldn't coopt one of the existing operators (for example, by making classes have a namespace for their methods)

Couldn't they provide a clearer explanation than simply dumping a huge IRC log like that??

Basically namespaces operate at a different level. You can almost imagine it like Macro expansion -- the namespaces are fully resolved for all the symbols in the file and then the compilation happens. This is necessary for a host of reasons. They can't co-opt an existing operator because all the existing operators work at an entirely different level.