As if anyone was ever harmed by such books.

Children's literature can still be judged on its pedagogical merits. Not all books are good, and that's why we have book reviews and experts writing recommendations for which books can be worthy additions to the school curriculum.

Heartstopper happens to be a work with quite high pedagogical merit because it approaches sensitive issues with tenderness, age-appropriateness and responsibility (especially when medical themes are explored in the story).

But some books can be potentially harmful and they shouldn't be read by children still learning about the world, especially if they don't have access to other reliable sources of information to counterbalance the bad information of some books.

To talk from personal experience, when I was growing up as a young gay teenager in a conservative country where there was no sex education in schools (at all, not even straight sex education) and no public real or fictional healthy models of queer relationships available, my only source of representation was yaoi manga that seemed to end up in the general comics book section of a chain bookstore. Even the non-pornographic manga did give me extremely harmful ideas about how relationship dynamics between two men might look like, both romantically and sexually. I did suffer real harm later on when as an older teenager I began dating, and the contribution of reading bad representation is not trivial to that.

For my younger self, I wish that I did have access to good books like Heartstopper, and someone informed enough to tell me that I shouldn't be reading the bad books until I was mature enough to understand why they are bad and how healthy relationships look like.

Hungary's law of course doesn't care about queer youth getting access to good books and avoiding bad books. Hungary's law just wants queer youth to disappear.