(From: https://www.grc.com/sn/sn-422.txt - about two thirds down.)
I figured I would share a bit of the philosophical basis I use to explain why privacy is necessary: The 20th-century existential philosopher Jean-Paul Sartre asserted that privacy was necessary to make the most out of our lives. This is apparent in his play "No Exit." In this play, a group of people have their eyelids removed and are trapped in a room together. It turns out this room is hell. This is where the quote "Hell is other people" comes from, he says. Their eyelids being removed is so that they can't even close their eyes and imagine that they are alone.
In Sartre's version of existentialism, he claims that humans have two modes of being: being-for-itself and being-for-others. Imagine you're alone in the woods or going for a stroll in the park with no one else around. You look at all the trees, the park benches, and leaves on the ground, and just enjoy the nice scenery. Since you're alone, you almost get the feeling that all these things are there just for you. You perceive these things as objects in your universe. This is being-for-itself.
Then suddenly, you notice someone else in the distance walking towards you, though they don't see you yet. Seeing someone else and realizing they are about to approach you, you now perceive yourself as an object in someone else's universe. So what do you do? You suddenly become conscious of your appearance. You make sure your shirt is buttoned, you fix your hair, you straighten your posture so you look presentable and mentally prepare yourself for an interaction with another person. Then, when the person finally approaches you, you put on a smile, claim you're happy to see the person, and extend your hand for a handshake. In this mode of being, you are viewing yourself as an object in someone else's universe. You're not just behaving as your true self, but you're also behaving how you believe the other person expects you to behave. Viewing yourself as an object in someone else's universe is being-for-others.
Sartre believes that being-for-itself is the mode where humans can be the highest form of themselves and make the most out of their lives. Being-for-others is the source of all shame, embarrassment, and guilt. People who live through the expectations of others and always behave how they believe others want them to behave is what Sartre refers to as being in bad faith. The philosophy is somewhat derived from Friedrich Nietzsche's concept of "bermensch," which is German for "Superman." An bermensch is someone who is the highest form of themselves with minimal influence from society. An bermensch is always living inside their own head, and they don't view themselves through the eyes of others. An bermensch also doesn't follow any rules or social norms that they don't understand, and make the most of their existence before they croak.
Ever since the whole NSA surveillance fiasco, I realize I'm always considering how I appear to others. Whenever I am talking with a friend, I have trouble getting the feeling of flow, in which I feel like I can be my true self, because I always know someone else is watching. It's like I'm always viewing myself through the eyes of a third party. Before every sentence I speak or write, I enter being-for-others in which I consider how I would appear to someone else listening in on the conversation. It's like I'm always behaving how the government would expect me to behave as the perfect citizen. I even find myself afraid to say inside jokes I have with my friends because I'm afraid someone listening in would take them out of context. I find myself constantly restrained from being my true self.
When the whole PRISM thing got leaked, I could hear Sartre and Nietzsche rolling in their graves. This news made me realize that existentialism is now more relevant than ever. If we believe we are always being watched, we will lose our ability to maintain being-for-itself, and we'll all be living through being-for-others in which we spend our short lives as robots behaving through other people's expectations. This is why in the opening chapter of "1984," Winston Smith sat in the corner of the room as he wrote in his journal, outside of the view of the cameras. He needed to escape the view of others in a desperate attempt to retain his humanity.