This is a gross simplification. Let's expand this discussion to public verses private. I'm going to talk about education instead of the USPS because I know more about education. Goal of a public education system: provide actual learning, understanding, and life-long skills to everyone. Goal of a private education system: maximize profits by providing competitive diplomas as cheaply as possible.
See the issue? The priority in the private system is on making profit and providing diplomas to people. The priority in the public system is on actual learning. The rampant grade inflation at Ivy League schools is a great example of learning taking a back seat in favor of producing graduates that look good on paper.
Don't make the mistake of thinking that "public" universities are any better. At my university (UIUC), research grants account for the vast majority of the funding for the engineering college. Consequently, research is the priority, not the education of the students. Simply put, the priority is where the money is. If the money is tied to the learning of the students, the students will actually learn. If it's tied to producing diplomas or publications, that's where the priority will be placed. UIUC can get away with it because its engineering graduates are still extremely highly paid. The prestige of UIUC's faculty is responsible for that, but it would be erroneous to attribute it to the educational curriculum. I can tell you from personal experience that the vast majority of graduates are average programmers at best and many haven't really internalized essential CS skills like algorithms, data structures, etc. One example that really sticks out in my mind: I went to a talk by Alan Kay last semester. Hardly any undergraduates attend, or even know or care who Alan Kay is. Alan puts up a few slides with pictures of McCarthy, Sutherland, Church, etc. Not a single undergraduate can name their primary contributions to the field. No one even knew the importance of Lisp! As Alan aptly put it, "you all are lucky your field isn't Physics; if it were you would be kicked out of the department and sent back to high school for not knowing the fundamentals of past research" (paraphrasing).
So why doesn't your grocery store example hold up? The success of a grocery store is strongly coupled to the quality of its product. Spoiled food is spoiled food. Education? Turns out the diploma, not learning, is what matters the most. The USPS is a similar situation, true value of the service (essentially free communication for all citizens everywhere) is only loosely coupled with the financial success of the service.
I went to public schools. The goal seemed to be keeping young people off the streets while their parents were working while also "creating jobs" for dozens of unionized schoolteachers of varying, often poor quality.
Some government programs accomplish a useful goal, and the USPS is one of these. But many government programs accomplish goals which are orthogonal or counter to their stated, useful purposes.
It's interesting. When you simplify USPS as essential service, it's fine. But if I take your 'essential service' argument and simplify it even further, I am doing 'gross simplification'.
Please don't even get me started on public education in United States. I would gladly allow 3 more USPS organizations to waste taxpayer's money if they get rid of public schools and adopt a school voucher system.
Please look for 'Stupid in America' show on YouTube and watch it. It will seriously change your opinion about public schools. Also, how many times have you heard people moving to certain district because they have better public schools? Have you ever heard anyone moving to certain district just because they have better grocery store?
I fail to comprehend why you think profit motive is a bad thing. Just like a private school has a profit motive, the customer (parents in case of private schools) have an incentive to get best value for their money and trust me, they will.
Please look for 'Stupid in America' show on YouTube and watch it. It will seriously change your opinion about public schools.
I'm aware of the documentary, and as usual, it completely misses the point. I'm intimately familiar with the inner workings of America's public and private schools (both the best and the worst on both sides). For the past several years I've had daily exposure to pretty much all angles of this issue. I suspect you've simply watched a 45 minute Youtube video and liked how microfoundations sounded when it was taught to you in school. I could write for hours on the horrors of private school vouchers alone (did you know when they tried it in Arizona, 3/4ths of the money ended up going to students who were already in private schools? [1]). And lets not even get into the fact that private schools actually don't perform that much better than public schools [2] when you account for the diversity in public schools. Considering that private schools mostly teach to a homogeneous student body, they should be blowing the public schools out of the water. They're actually not that much cheaper either, when you consider that private schools don't need to spend nearly as much money on special education programs and psychological therapy [3]. If I was a school admin I could post the most impressive numbers in the country if I'm allowed to skim from the cream of the crop, but public schools by law are not allowed to do so. However, I suspect at this point expending any more energy on this issue wasted effort since you seem dead set in your ways.
See the issue? The priority in the private system is on making profit and providing diplomas to people. The priority in the public system is on actual learning. The rampant grade inflation at Ivy League schools is a great example of learning taking a back seat in favor of producing graduates that look good on paper.
Don't make the mistake of thinking that "public" universities are any better. At my university (UIUC), research grants account for the vast majority of the funding for the engineering college. Consequently, research is the priority, not the education of the students. Simply put, the priority is where the money is. If the money is tied to the learning of the students, the students will actually learn. If it's tied to producing diplomas or publications, that's where the priority will be placed. UIUC can get away with it because its engineering graduates are still extremely highly paid. The prestige of UIUC's faculty is responsible for that, but it would be erroneous to attribute it to the educational curriculum. I can tell you from personal experience that the vast majority of graduates are average programmers at best and many haven't really internalized essential CS skills like algorithms, data structures, etc. One example that really sticks out in my mind: I went to a talk by Alan Kay last semester. Hardly any undergraduates attend, or even know or care who Alan Kay is. Alan puts up a few slides with pictures of McCarthy, Sutherland, Church, etc. Not a single undergraduate can name their primary contributions to the field. No one even knew the importance of Lisp! As Alan aptly put it, "you all are lucky your field isn't Physics; if it were you would be kicked out of the department and sent back to high school for not knowing the fundamentals of past research" (paraphrasing).
So why doesn't your grocery store example hold up? The success of a grocery store is strongly coupled to the quality of its product. Spoiled food is spoiled food. Education? Turns out the diploma, not learning, is what matters the most. The USPS is a similar situation, true value of the service (essentially free communication for all citizens everywhere) is only loosely coupled with the financial success of the service.