To play devils advocate, App developers will loose revenue from ads as they're not as efficient at showing ads users are likely to click on. Those developers may change their business model from 'free - ad supported' to 'features locked behind an in-app purchase' which Apple receive around a 30% cut of.
I personally don't feel strongly one way or the other, both contain shady practices.
There's three independent issues here affecting users and developers:
1. People are tracked in ways they don't understand without their knowledge or consent.
2. Apple requires that in-app purchases go through the App Store.
3. Apple does not allow 3rd-party app stores.
These can all be independently tackled and it would be a shame to gate solutions for one problem on solving the others first or at the same time. For now, apps can change their business models to ensure profits. Later, when the other issues are taken care of, they can take advantage of that as well.
