I don’t think what you’re describing is wrong. But a belief that something is a natural monopoly causes us to make policy choices based on a flawed assumption. Flawed choices about the inevitability of a monopoly tend to entrench same.

E.g. our municipal broadband monopolies trace back to a belief that wireline phone and TV can only be monopolies. And maybe it’s true! But we might have chosen differently, had we not assumed it a natural outcome.

We might have assumed that wireless is a natural monopoly. Gladly, we didn’t. (Though spectrum policy can be more competitive.)