I don't see what the problem is. If the User doesn't want Gemini to read his or her messages, the User doesn't have to partake in the sending of the messages. Simple! A User agrees to be bound by the ToS (Terms of Service) in having they do take to receive the user agreement as bound in law by Google. The User doesn't need to understand or have the right to contest the agreement or the use of any data created by a User, as the User can simply not use the product or service as governed by the same Google ToS. Simple!