[bo1024]

Agreed. There is an additional simple point of view which I believe clarifies the situation, which is to look at the total costs and total "value created" ("social welfare") under different systems. In other words, you ask what is the "first best" and what system can achieve it.

Consider selling wheat. If one company owns all the wheat fields, or the wheat fields are evenly split among two companies, the total amount invested in growing wheat is the same. And since multiple companies means competition, lower prices, and more consumers served, having multiple companies is more efficient in the econ sense (higher social welfare = total value - total cost).

But with fiber infrastructure, having two copies of the infrastructure is a huge waste of total resources. It is far more efficient to only have one set of wires. The problem is if they are controlled by a monopolist, they will keep high prices and serve fewer people. So a single copy of infrastructure with a monopolist is sub-optimal, but so is multiple copies of infrastructure with competition. Optimal is a single copy of infrastructure along with regulation or some other means of keeping prices lower than monopoly.

Of course, you can still try to implement market competition over those wires via regulations that force companies to share the wires, etc.