"(Craigslist) said it offered a license that would have allowed PadMapper to use its data on mobile applications but that the competitor did not accept the terms." But on the other hand, "users and developers are exasperated with Craigslist’s insistence on preserving an outdated interface and design." I don't know the legal merits of either party's position, but from an ethical perspective, I tend to side with Craigs…
Craigslist has no divine right to its users' information; it just happens to be the only viable option. If Craigslist didn't exist, someone else would, and would probably do it better.
If Craigslist wants to continue existing, they should take advantage of the fact that they are the go-to for online classifieds, create a modest subscription-based API and let the information flow.