The crux is essentially this
State owned vs. private is NOT the central question in how you organise railways
You need to ask WHAT you want to run, FOR WHOM, and AT WHAT PRICE - and answer that *politically*
WHO IS A RAILWAY FOR?
Then you work out how to organise it - with state firms, private ones, open access, competitive tendering, integrated operations etc.
@jon Indeed, and you're right: The political question is whether you want line xy to be cost-returning or if you're willing to subsidise it.
However, that political decision (e.g. minimum service level) flows directly into a tender. If done correctly, that tender will return a winner that will cost more than break-even and require subsidies.
What you then see might be scrapping of the whole project.
But what happens more often imho is that e.g. the service level isn't appropriately defined in the tender, and the winner is then the one staying below or close to the break-even level cost-wise. Then, upon the next evaluation, the line is under-used (because it has crappy service) and the result used as an excuse to cut the maximum accepted cost level even further - or to close the line completely.
So, I agree with you, that it's a political question. But I'd say the quality of the tender process is just as important mid- to long-term.
@cweickhmann Yes, sort of. But lots of what's done in railways is not organised that way. There is no Ausschreibung for what DB Fernverkehr runs for example - that is meant to be cost-returning.