> complete unaccountability of a government monopoly.
That is a problem with the quality of your democracy, not with government monopolies. A corporate oligopoly is virtually identical to a nondemocratic governmental monopoly.
Democracy is not a mechanism for accountability. No democracy can produce accountability, that's not what it's for. A company with competition has a degree of accountability because their customers can go elsewhere if they are mistreated. A citizen without a lot of money to spend on political campaigns have very little recourse when they are mistreated by the government. Even when the government breaks its own laws, there is almost nothing you can do between qualified, absolute, and sovereign immunity.
The US and other governments have long histories of medical abuses. I would not want an organization that preforms unnecessary and intrusive surgical procedures without consent[0], falsely told people they have cancer in order to remove their reproductive organs[1], intentionally gave people syphilis, hepatitis, and other diseases[2], pretended to treat syphilis to see what happens when it's left untreated[3], etc. to be my only provider of health care. It frankly seems irrational to want an organization that can act with impunity and seem to abuse every function and responsibility it is given to be the sole provider of anything.
That is a problem with the quality of your democracy, not with government monopolies. A corporate oligopoly is virtually identical to a nondemocratic governmental monopoly.
The key thing you want is democratic control.