Should Craigslist be subject to liability for FHA violations?

Question 1:
Immunomedics was alerted there was some negative buzz about the company in a chat room.
The poster used a pseudonym and therefore the company was unable to identify the poster for lawsuit purposes. The only information the company could ascertain was the poster's ISP. So the company decided to subpoena the ISP for identity information of the poster in order to file suite against the poster.
How should the courts handle these cases where the company's complaints may, or may, not rise to the level of an actionable legal claim?
Question 2:
Should Craigslist be subject to liability for FHA violations? Why or why not? Cite appropriate legal principles when explaining your answer.