Depends on the jurisdiction of the website. In the US, it is protected by the section 230 ("no provider [...] of an interactive computer service shall be treat

Depends on the jurisdiction of the website. In the US, it is protected by the section 230 ("no provider [...] of an interactive computer service shall be treated as the publisher or speaker of any information provided by another information content provider"). In other words, you can sue the commenter, but not the platform hosting the comment. In the EU, there's an opposite precedent (Delfi AS v. Estonia), in which the European Court of Human Rights (ECHR) confirmed that fining Delfi (Finnish web portal) for comments doesn't go against the platform's freedom of speech. Of course, that's not a law, but it might impact future EU-wide laws that aim to regulate that sort of thing.