I can't lie, as soon as I saw the headline "Most detailed image of Uranus..." on my FB feed, I began chuckling to myself. I know, I'm a child.

By your logic, if someone has a public conversation in Chinese, it should be illegal to listen to them since proficiency in the Chinese language is "special knowledge".

If you chose to send your personal information via Wi-Fi, cell phone, or other radio signal, you are sending that information as far as the signal will carry it to whomever is in range. If you were having a loud argument in your apartment, would you expect your neighbors to not listen in? If you send your personal information through someone else's private domain, or through the public domain (whether it is via sound wave, electromagnetic wave, or whatever), you have no reasonable expectation that people within range to receive that information aren't listening to it.

Hardline telephones are completely different as the lines themselves belong to the telecoms. If someone taps a phone line, they are tapping the phone company's private property. If you decide to broadcast to everyone in range, that's your problem.