What then, does the USPS do that is essential to the functioning of modern society? While it certainly employs a lot of people who need jobs in post offices and on the street, the basic answer is "nothing."
The goal is to have a public Postal Service that can compete effectively in the market. But it's not a fair fight when we shove it into the ring with its shoes tied together and both hands tied behind its back.
There is an alternative to the current flood of crocodile tears over the death of written communication. We could return to the social compact that regarded mail service as something to be paid for by the people who benefit from it most.