As for your kitchen example, you don't need to say anything. Walk into any room with a weapon and people will know they might be in danger. If I'm in that kitchen, and you walk towards me, I'll move out of arm's reach.
Basically it's the same problem: Assurances are worthless. Rationalization provides seemingly excellent reasons for any course of action. So, the onus is on you to show that no harm will be done. It certainly is not the responsibility of some 3rd party to establish this, that is a coercive worldview.
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.