Libel isn't about how unkind or hurtful a comment is, but how much it damages somebody's reputation. Jack Monroe has a public reputation. Although Hopkins deleted the comment when she realised the mistaken identity, it was retweeted, Hopkins refused to issue a disclaimer or apology and people believed the original tweet. Keyboard warriors sent Monroe hateful and threatening comments, because they believed what Hopkins had written. It's absolutely right that this kind of 'fake news' should be stamped on by the law. Even now, Hopkins is tweeting snide and nasty comments about the case.