The thing is, there's no way to prove you won't do something in the future if you have the ability to do it. All you can do is promise that you won't, preferably in a legally binding way (such as a privacy policy) and stake your reputation on it. That's the basis of society. Just because someone doesn't believe you doesn't give them the right to force you into a false confession.

The app developer says "all your contacts stay on your phone, we only use the internet for calls". Google says "this app is able to access both your contacts and the internet any time for any purpose". Both of those statements can coexist and be presented to the user for evaluation. The app being required to pretend like it's uploading your data is just lying to the user.