Now you are using the legislators' rationale that money is being made so we need to protect that, forgetting to weigh the cost for the community.

That's an outlier. Most works don't see so much public interest after such a long time.

But why should this be allowed? Fairy tales are still popular, but they don't have copyright either.

It would make sense to make it possible, but increasingly expensive to extend the copyright. It's fine for Disney to keep their successful creations, it just makes no sense to drag all other copyrighted works in existence along for the ride.

I'm not sure what your point is. Harry Potter is in the top ten highest grossing media franchises ever. Sure, top 10 franchises make a lot of money, but they're outliers. Is it in the public interest to grant every author in the country a copyright monopoly for life + 70 so that we can ensure JK Rowling's grandchildren continue to make billions from Harry Potter? Clearly not!