[kscaldef]

That information isn't all that useful, since UPS and FedEx don't compete (and are forbidden to compete) in the marketplace for mail (as opposed to package) delivery. Regardless, though, I'm making a very modest claim: competitors would take away part of USPS's marketshare if they were allowed to compete. If you feel like there's a natural monopoly on mail delivery such that that wouldn't happen, you need to support that assertion.

[hga]

Well, there's the cherry picking argument, something we can see with broadband build outs.

E.g. they'd offer low low low rates for delivering snail mail on Manhattan Island and leave it to the USPS to handle mail in Eagle Butte, South Dakota.

Hmmm, didn't AT&T do the same back in the bad old days?

[kscaldef]

So, you agree that competitors would take part of USPS's business. That's all I claimed.

[hga]

I claim your thesis has a critical corollary that goes beyond "competitors would take away part of USPS's marketshare if they were allowed to compete". Specifically that the competitors would cherry pick the most profitable business of the Post Office and force it out of business leaving much of the nation unserved, or into a business model we don't think would be good for our society (first class mail to Eagle Butte, SD costing, say, $10/oz).

There's also friction issues. If I'm going to send out every month a set of bills to my customers, I know the cost will be X customers * the rate I pay (which I can decrease by making things cheaper for the USPS),