If a company has a monopoly on data and refuses to provide an API they're saying that they don't want to compete on the quality of their productThis implies that part of the quality of a product is NOT the ability to gather data. This would be like me walking into a Walmart, setting up a cash register next to theirs and start ringing up customers and arguing that Walmart can't compare with my customer service. Ignoring that customer service is just one small part of the business. Walmart had to find the property, buy the property, do the legal work to get the product on the shevles, the negotiation, the supply chain management, etc... I can't just focus on the last mile and then argue that I'm entitled to everything else they did.
Craigslist built its name, it's reputation, it's backend, it's API, vetted a business model for its services, scouted out regions to focus on etc...
Furthermore, people are arguing the data is the users, not CLs. True, but the user gave it to CL, not to you. When I loan books to a neighbor I assume they aren't going to create a library of my loaned books (unless they specifically told me so).