Please cite specifically what you're referring to as "political propaganda". Is it the claim that students don't have much of a choice when it comes to public schools? If so, to call that "political propaganda" is absurd.
Regarding Seattle, you're citing one data point. The majority of American public schools don't operate with open enrollment. If you're in a public school, you're assigned to one school in a designated area, and can't choose a different school.
"Go to Watts and check out the selection and quality of food in supermarkets."
This is just completely false and dishonest. There are a handful of Walmarts and Targets around Watts and the majority of other low-income neighborhoods -- all within a 5-minute drive.
The "appeals to authority" fallacy applies when I'm citing non-experts (like if I'm citing Chomsky for an economics issue). CATO is overwhelmingly filled with PhDs in Economics, and with my economics background, I think it's safe to assume the above article is not controversial at all among economists across the aisle and none of them would term it "purely political propaganda".
You state that CATO is "purely political propaganda" without substantiating that claim with any specifics whatsoever. Where is your data?
American public schools, with few exceptions, don't compete with each other for resources and students. Therefore, it's a form of monopoly. For instance, an American student within a designated area can only attend a certain public school. Geographically-disadvantaged residents can still choose supermarkets outside their areas if they find more utility doing so (or a competitor can start up their own supermarket and take market share from the lazy incumbent), so supermarkets do exist in a competitive market. Public school students rarely have the option to choose new suppliers.
Well, only 2 are dead, and those two (Hayek and Friedman) are probably the most famous libertarian economists/thinkers. I think it would be safe to assume they would support the article above.
"the Cato free-market spin is questionable and not terribly well suited to Hacker News, IMO"
Sorry, but you dismiss Cato because of its "free-market spin" and then call its main thesis "questionable", when 10 Nobel Laureates, who probably know far more than us on economic issues, are associated with Cato. I'd also note that Paul Krugman, Delong, and Sachs -- all very prominent Democratic supporters -- are very pro free market as indicated on the links you'll find on their Wikipedia pages.
Why would you automatically declare an organization like Cato, which comprises a lot of living and dying Nobel Laureates (10 in fact) and read by a large number of PhDs in economics from our top universities, not HN worthy and "political propaganda"? It's a little absurd to make such a claim without substantiating your argument.