No. I might be inclined to agree, if it weren't for network effects. Once a company reaches a certain size and market share, like Craigslist, would-be competitors are at a competitive disadvantage. Lots of people have created objectively better sites than Craigslist, but they fail because of network lock-in. Normal capitalistic competition is failing. This is the same thing that happened with railways, utilities, and…
There is no lock in. A buyer or seller is free to move place their listing or make their purchase from any number of alternatives regardless and Craigslist can't stop them.
> Sites like Craigslist and LinkedIn have become the new natural monopolies.
Mark Zuckerburg would probably disagree with that statement. In 2005 MySpace would have been the equivalent of Craigslist, massive network, shitty design and no data portability. If the value provided by alternatives to CL were as superior as most HN readers believe them to be then END USERS would see that as well and migrate just like MySpace users migrated to FB. But they don't so CL retains its dominance, the failure of alternatives is not indication that CL is cheating or doing anything even remotely monopolistic.
> And demanding that they open up their data is the natural, and right, action to bring back natural market competition that benefits consumers and the world at large.
The data is open, just not in a format you think you are entitled to it in. It's open in that the same poster that put their listing on CL can post the same listing on alternatives, they just choose not to. Convince the seller or buyer of the value you bring to the table and they will open their data to you as well.
Many HN readers have reached the conclusion that convenience and competition are the same thing. They aren't.