It is easy in principle to decide whether something should be left to private enterprise or public service. Simply ask five questions:
(1) Is the service or product generally considered to be a necessity?
(2) Will profit compromise safety?
(3) Is the service obviously inappropriate to be left in private hands, for example policing or defence?
(4) Can the service be provided by private enterprise without subsidy?
(5) Can free enterprise be reasonably expected to deliver the necessity universally?
If the answer to any of (1)(2)(3) is YES or the answer to either (4) or (5) NO, then it should in principle be provided either directly or indirectly by the state.