You wouldn't let that happen in real world
Would you allow a stranger to enter your home, and look around?
When you send an email, it’s like a postcard, several agents (digital and human) copy and read it on the way. Would you accept it in real life?
Why accepting this in your digital life?
Rules are changing
In the past, rules of countries have changed drastically, for example the concept of freedom. Future changes might affect your future self. Your present privacy is important for future freedom.
If you took the most paranoid person from 5 years ago, after everything we learned recently about spying on the Internet by governments and companies, that person was actually right.