It's not necessary. Nouns-as-categories is a misunderstanding of language; an extremely common mistake that people make when studying language, but never when fluently using language. Half of philosophy is based on (and rendered completely pointless by) this mistake. It's just a case where people's own intuition about how they're using their own language is faulty. Perhaps I should have said "it's difficult to use language without being accused of relying on categories". Ontology came way way later in human thought than natural language did.