You can run an access point with all the benefits of WPA2/AES, but make the password really simple. Setting your SSID to "PasswordIsBacon" or just using the same SSID and password is a fairly easy way to share access, without running a completely insecure, unencrypted network.
That's "easy to share" which is a much greater hurdle than "publicly accessible". I want strangers to be able to use my wifi in the middle of the night from outside my home. I want devices to connect without any questions or hassle.
