The U. S. Constitution merely says that "The Congress shall have the power … to establish Post Offices and post Roads;…"
Does "establish" mean "set up" or "operate"? How is it financed? Should it be self-funded or are Post Offices" part of the "General Welfare"?
All we know is at the time of the writing of the Constitution, the only means of communicating were either face-to-face or putting words on paper and sending them to other people. One of the means of putting words on paper was called "newspapers", and the Founders considered newspapers so important to having an informed citizenry that they subsidized the postal delivery of newspapers (Post Office Act of 1792). So, from the beginning, the Post Office was not self-supporting and was not intended to be.
The writers of the Constitution did not foresee the telegraph, the telephone, the Teletype, radio, television, and the Internet; all means of expanding the distribution of information (or misinformation). Maybe the Internet should be subsidized to have an informed citizenry. Of course, it is subsidized in a way. Government organizations from local to international provide websites for public access to information. But these sites are maintained by government employees.
We do have a slightly subsidized Internet - it's called public libraries, many which have free, albeit limited, access to the Internet. Of course, free libraries and free Internet require taxes, which we can have none of.
What a long way we've come from
“However firmly liberty may be established in any country, it cannot long subsist if the channels of information be stopped,” Massachusetts Senator Elbridge Gerry stated in his fierce defense of providing federal subsidies to newspaper postal distribution in 1792.– "The History of Transparency – Part 1: Opening the Channels of Information to the People in the 18th Century"
BTW, we have the wish to limit information all over the political map. The Obama administration want to get authority to eavesdrop on the Internet. See "U.S. Tries to Make It Easier to Wiretap the Internet", Charlie Savage, New York Times, 2010-09-27.
Again, where are the strict constructionists?