You're right that the deficit is mostly artificial, but since this has come up a lot recently it's important to point out that the USPS as an entity is not enshrined in the constitution. The postal clause says:

> The Congress shall have Power...To establish Post Offices and post Roads

And that's it. The rest is left up to Congress to figure out; they could, if they chose, punt entirely and allow eg FedEx to run post offices. I think the USPS is vitally important, and we can make arguments for its role as a public good without being hyperbolic about it.