Anyone in that position would think the app is shady AF and user hostile.
It's not necessarily shady or user hostile when done right, and there are plenty of opportunity to add trust relationship building as a part of the consent process (links to privacy policies; details about marketing policies; etc).
It's also not that different from how many iOS applications (at least) are encouraged (in App Store best practices) to handle consent models for location tracking and notifications: ask the user as they become familiar with the application, not up front, and provide as much context as you can.
That said though, I don't see why the app couldnt just change their sharing model to an "invite link" based pattern. If I want to share something with a friend, why do I need to provide their private information to the app to do it? Why can't I generate an invite link and send that through my already established channels of communication? I don't think the "but your friends don't know your Apple privacy email" reason is very compelling. That might not work in their current system, but it is definitely not an insurmountable problem.
