Be angry then, IM communication is not a contract with terms unilaterly decided by one party. Or put a confidential signature with every message, see how well that works for you
If I need a contract for you to treat me decently and respect my choices, I really dont think you can count as a "friend" at all.
Be a better person. Or at least put a message in your status that you record everything and send it to Google for analysis for minimum personal gain. Do you also carry a second phone to take a photo just in case someone sends you a disappearing photo?