Without getting into the ethics of animal husbandry, how does one explain to a vegan that the wool of a domesticated sheep MUST be shorn by a human being, as selective breeding means that most domesticated breeds cannot shed naturally?

Without getting into the ethics of animal husbandry, how does one explain to a vegan that the wool of a domesticated sheep MUST be shorn by a human being, as selective breeding means that most domesticated breeds cannot shed naturally?