At what stage does a mercantile product become a necessary public service?

Interesting one for any privatised service, although with what I know from the past (under Post Office telecommunications everything connected needed a BABT licence, takes years to get blah blah) we would never have broadband if it wasn't for the opening up of markets.

One assumes a responsible government would insist a market around a monopolist infrastructure would be include safeguards against passing the buck?

No, silly me.