What tax dollars are you talking about here? The USPS is only in the red because of congressionally mandated pension funding requirements. It’s a business otherwise. Not sure why everybody’s talking about tax dollars.
They are required by law to fund 75 years of their pension obligations. Because of this, they run in the red, not because the business model is completely flawed.
Further, rural routes are things that should continue but are cost prohibitive without subsidies. With those two considerations combined it seems like a pretty meager use of taxpayer dollars.
https://about.usps.com/newsroom/national-releases/2019/1114-...
That said, allowing them to set rates will likely help the bottom line a great deal, but the USPS is a business.