Copying is not stealing! Christ, the music and movie industries have really fucked up the meaning of that word in recent years.
Any service competing with Craigslist that uses those classifieds might not be stealing them, but its certainly in Craigslist's best interest to keep their most valuable asset safe.
I'm simply saying that Craigslist has a vested interest in keeping their data/facts/ads/whatever on their platform.