That's reading a whole lot into the definition of "free." Were people "free" in 1950? If so, how do they become "not free" by introducing a new form of communication (created by the military, mind you) that is monitored more heavily than the ones they used to use?
Aside from the technology aspect, there was no Patriot Act and it would at the very least be difficult to detain citizens long term without charges. Sounds less free to me.
G = Percent of people that the government can spy on for a form of communication (0-1 where 1 is everyone, 0 is no one).
D = Percent of personal data that gets sent using that form of communication (0-1 where 1 is everyone, 0 is no one).
G * D = Freedom Lost.
Using made up but reasonable numbers
Mail = 0.05 * 0.001 = 0.00005
Email = 0.4 * 0.99 = 0.396
Historically mail was used for almost all personal data but the capability to spy on mail was far lower (d= 0.8, G = 0.000001). As time increases communication privacy goes to zero (since both G and D will increase as an average over all means), unless, of course, the trend changes.