While homeschoolers support the rights of parents to direct their children's educations, "unschooling" in it's purest form is controversial even among many homeschoolers.
The more common scenario is that homeschoolers have some more directed studies (math, science, history, etc...) and the child explores other areas in an "unschooling" way... reading for instance. My kid has some required reading, but is free to read anything he'd like, and that is a wide range of material. He likes sci-fi books, and reads them to his heart's content with our blessing.
I don't know any homeschoolers (personally) who are fully onboard with "unschooling" for every discipline.
Which is the whole point of the national curriculum. Here is a set of facts and data that every school child should be familiar with and problems that every shcool child should be able to solve before graduation.