Earlier quoted context omitted.
The problem is these companies are too big and powerful now. If a small business refuses someone its no big deal, go to another business. But when these titans join together to make an action that affects you and there are no alternatives left, thats a different case. If both Apple and Google ban your app when the app is legal and useful, is it good for society that there is no way around this?
"Legal and useful" are but two criteria Apple uses to approve or refuse apps. They also care about safety, performance, and design. https://developer.apple.com/app-store/review/guidelines/
IMO its fair for the app store to remove whatever it wants but there needs to be an escape hatch where apps blocked by apple can be manually installed. Since the API apps have access to is secure, this should not be a significant issue.
Apps like Parlor may be full of ToS violating content but users should still be able to sideload the app and the government should be the one to shut them down if the content is illegal.