Not always if the slanderer is in another country.
I had someone online who was claiming that I was really someone else and involved with some people in illegal activities. She said she was going to contact every company I worked with to tell them of my "illegal dealings." Luckily, I a) only used a pseudonym there (unlike on Slashdot), and b) the woman was certifiably nuts. As evidence to the latter, she claimed that she was a prophet of god. Her proof of my "illegal dealings" were that god told her so. Any sane company would immediately file her complaint to the trash.
Someone else who she pestered (actually the person she claimed I "really" was - her proof? We both liked photography) had his real name and employer online. She contacted him, his employer, and all of his relatives on Facebook (along with anyone who might happen to share the same last name). Given that he is a teacher, her charges involving kids could have caused him to lose his job. Thankfully, he warned his employer about her and they ignored her.
A bunch of us who were harassed by this woman have contacted the police to no avail. Charging someone with slander and harassment from another country is very tricky. Not only that, but when she finally harassed someone in her own country (Canada), the person filed suit... and the police went to her house and told her just who was suing her. Like telling someone charged with harassment who is fighting back ISN'T going to result in more harassment. As far as I know, that case went nowhere. It got tied up in the legal system for a bit before petering out.
So this woman is free to harass more people as she sees fit and our options are limited.
(This isn't meant to say that "Right to Forget" is good. Just that existing laws might not be enough.)