The vast world of knowledge has enough nooks and crannies to satisfy everyone. It's rather amusing to hear people suggest that a child following a passionate interest is somehow being cheated. The real joke comes, of course, when someone tries to explain how a narrow interest means missing other branches of learning. In reality, learning only one thing at a time is impossible. Dividing the world up into sections to fit into a notebook is an artifact of school's needs to have a labeled curriculum.
Real life flows, with different areas of knowledge meeting in unexpected ways.
For many, the notion of self-motivated learning contradicts their experience of young people. Sure, some kids may exhibit less willingness to do what grownups think is constructive than others. Without active interference, simply supporting a child's interests and making materials available is enough. My child wants to explore the environment around her. We aren't passive agents, either.