Prefunding medical pensions is not the reason for their cash flow problem:
> In addition, with respect to financial reporting, here are the key figures for 2019:
> Healthcare benefits paid out of the Benefit Fund: $3.7 billion.
> Normal costs scheduled to be paid into the Benefit Fund to cover current year’s current employees’ retiree healthcare cost accruals: $3.775 billion.
> Amortization payments scheduled to be made into the fund: $789 million.
> Overall net loss for the year: $8.8 billion.
> The math just doesn’t work to blame retiree healthcare contributions for the USPS’s losses. The amount they are recording on their P&L for retiree healthcare costs (which, again, they aren’t paying out in cash) — $4.564 billion — is only moderately more ($800 - $900 million, depending on rounding) than the amount that they would be paying out directly for pay-as-you-go benefits had the PAEA never been implemented.
https://www.forbes.com/sites/ebauer/2020/04/14/post-office-p...
And I actually do see this as a "because it's not A it shows it is therefore B" type argument. When the USPS runs at a deficit, tax payers ultimately are the ones that have to bail it out. That goes against the principal necessitating stamps in the first place: individuals who don't place extra cost to the USPS end up paying more than their share and subsidize individuals who do cost the USPS extra.