The author is British, and I think some of these points make sense in the context of the UK. You should see how screwed our privatized rail industry is - itself a kind of "natural monopoly". True capitalism would have the government stop subsidizing them; but then we wouldn't have any trains, and good people wouldn't be able to get to work. Too big to fail again, I'm afraid...
I interpreted the word "natural" to mean the monopoly was achieved and exists without government subsidy or special privileged. Capitalism says that the only time monopolies are ever "destructive" or have a "snowball" effect where they can't be stopped, is when the government gives them special privileges (i.e. no one else can build a railroad, no one else can set up a telecom company).
If the government puts up road blocks for new companies to enter a line of business, the market isn't truly free and the mega corporations are free to charge whatever they want and do whatever they want. It would be impossible for there to be a "startup" telecom company or "startup" railroad company.
Interestingly enough, the the railroad companies are the most often cited example what happens when the government messes with the free market. The idea is that because the government has already messed up the railroad market it has to continually subsidize the railroad companies or, you're right, "good people wouldn't be able to get to work". Regulation and subsidies beget more regulation and subsidies.
"natural monopoly" is economist's jargon. It is basic jargon. Every undergraduate economics text book covers it. Mankiw's Principles of Economics discusses it on page 306. Economics by Parkin and King cover it on page 296. Beardshaw sees to have something against the term, talking instead about "The flat bottomed average cost curve" on page 266. Alchian and Allen discuss natural monopoly on page 290 of Exchange and Production. Google it.
