If these were articles written by professional writers, you might have a case. Instead these are posts written by many different individuals trying to advertise their properties.
Craigslist didn't write a single one of those posts. They try and assert control over this content through their terms of service:
"You automatically grant and assign to CL, and you represent and warrant that you have the right to grant and assign to CL, a perpetual, irrevocable, unlimited, fully paid, fully sub-licensable (through multiple tiers), worldwide license to copy, perform, display, distribute, prepare derivative works from (including, without limitation, incorporating into other works) and otherwise use any content that you post. You also expressly grant and assign to CL all rights and causes of action to prohibit and enforce against any unauthorized copying, performance, display, distribution, use or exploitation of, or creation of derivative works from, any content that you post (including but not limited to any unauthorized downloading, extraction, harvesting, collection or aggregation of content that you post)."
The last part of that may not be enforceable. They're asserting that they are singularly responsible for "authorizing" reproduction despite not having copyright for the material in question.
Craiglist doesn't need to write those posts. Under their TOS, Craiglist has a license to the posts (which are copyrighted by their owners ). This license gives Craiglist the authority to enforce copyright against persons who interfere with Craigslists' license in the posts. Thus, the last sentence of their TOS is perfectly legal and enforceable. The license would not give Craiglist a license to do anything to other services on which the original posters also post their listings to. But that is not the case here.
They are plenty of cases where copyright enforcement is voluntarily handed over to a third-party: for example, Hollywood to the MPAA, or the BusyBox developers to the SFLC. Does anyone know what the difference is?
Righthaven is different. Righthaven did not have a copyright use license, so it did not have the right to enforce the copyright. (A copyright enforcement "license" is a non-license, legally, since it does not convey any actual copy "right" such as distribution.)
Craiglist does have a copyright use license, and thus has the right to enforce the license it has been granted.
Craigslist didn't write a single one of those posts. They try and assert control over this content through their terms of service:
"You automatically grant and assign to CL, and you represent and warrant that you have the right to grant and assign to CL, a perpetual, irrevocable, unlimited, fully paid, fully sub-licensable (through multiple tiers), worldwide license to copy, perform, display, distribute, prepare derivative works from (including, without limitation, incorporating into other works) and otherwise use any content that you post. You also expressly grant and assign to CL all rights and causes of action to prohibit and enforce against any unauthorized copying, performance, display, distribution, use or exploitation of, or creation of derivative works from, any content that you post (including but not limited to any unauthorized downloading, extraction, harvesting, collection or aggregation of content that you post)."
The last part of that may not be enforceable. They're asserting that they are singularly responsible for "authorizing" reproduction despite not having copyright for the material in question.