If I have a contract with the clerk at the grocery store, I would trust him. If he broke the contract, changed the terms, added new sections, etc, then I would

If I have a contract with the clerk at the grocery store, I would trust him. If he broke the contract, changed the terms, added new sections, etc, then I would have a reason not to trust him/her. That's literally like telling me I shouldn't trust my employers with my direct deposit info and my social security. Or that I shouldn't trust the insurance company with the same information, etc. How is a privacy policy, changed behind users backs, with blatantly offensive auto-opt-in/out features not a violation of a reasonable expectation?