By that logic, if someone uses a phone book to harass you via telephone, the phone company is liable.
Or, for a more up-to-date example, if someone uses a DNS provider to find a server's IP address and do a DDOS attack against it (as is constantly happening to KF), the DNS provider would be liable.
The phone book and DNS provider are different because they don't say why one would want to harass those people, whereas on KF that information is provided along with their contact info.
Or, for a more up-to-date example, if someone uses a DNS provider to find a server's IP address and do a DDOS attack against it (as is constantly happening to KF), the DNS provider would be liable.