They have a monopoly on what? Apps in the Apple App Store? I agree they shouldn’t be able to use their market dominance in the app marketplace space to stop other app marketplaces from competing with their App Store, but within their own ecosystem that is way too specific of a thing to apply anti-trust rules to. The reason the App Store is popular is because of the iron grip they keep on their apps. Telling them they can’t control their apps the way they want is like telling a chip maker they can’t use a certain architecture because it is too fast and other companies won’t be able to compete with them.

Specifically, because it harms consumers, it harms the industry (or industries in this case), and hurts innovation.