Oh well nevermind, if craigslist make a lot of money from doing something than I certainly don't want anyone else innovating and taking their business away. We as consumers need to fight for businesses right to never have to compete with anyone else and freeze others out of the market via legal threats.
No that's not really what it's like. They are using information from Craiglists site, even if you don't respect Craigslists claim to IP on the user-submitted listings you have to respect the fact that it's their servers/resources that collect and then re-feed that data directly to their competitors. They are perfectly within their right to stop that, not just legally but ethically as well... at least IMO.