The thing about socialism that transcends capitalism is use values--providing use values and making this the measure of success: nutrition, life expectancy, health outcomes, housing, etc.
Using these as metrics of success (along with general happiness) rather than abstract figures (GDP per capita [useless when inequality is high) related to exchange values.
With that said, the post office is an amazing use value: send letters virtually anywhere for less than a dollar, send packages across the world, union wages, etc.
We take it for granted because we've always had it, but it's an amazingly efficient and affordable service.
It's not supposed to be profitable, it's not supposed to be measured by capitalist metrics--that's why it's important to defend, as a use value, and to push back on the whole "run it like a business" narrative.
And this goes for other services the government does, like say, the British health service or even transport systems (we have this argument with WMATA in DC every year):
The right calls for the service to be self-funded, profitable, tied to a strict budget, certain portions to be privatized or subcontracted or oversaw by the private sector in some way, etc.
And then the mainstream "left" tries to meet them halfway by resisting privatization but introducing business methods to its daily...(+)
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