This is just another example of why you shouldn't base your startup on someone else's product. If you're successful, they'll develop a competitor and use their position to push you out.
So? They're still being a bully. Just because you're acting within the confines of the law and your rights doesn't necessarily mean you aren't being a dick about it.
This just puts you back where you started.
It's incredibly naive to assume you know best.
We have our job ads republished by job sites with user bases that are far outside what we're interested in, and it results in a massive waste of our time in filtering those candidates.
Apologies for resorting to profanity, but I find Craigslist's behavior completely odious and am continually disappointed to see so many on HN defending them. For a more articulate argument, see 3taps' claims of anticompetitive behavior: http://techcrunch.com/2012/09/24/3taps-files-craigslist-coun..., scribd document at the bottom, pages 25-30.