I think the essential point here is that offensive and slanderous comments should be allowed in the interests of free speech, provided such comments have a factual basis. It is up to the person who feels offended to take action within the law if he/she knows the offensive comments to have no factual basis.
Human nature is such that people can be offended by the utterance of true comments about themselves, or others whom they highly regard, so to ban all comments on the basis they could or might be offensive is simply not rational and democratic.
The great Irish writer and poet, Oscar Wilde, represents an example. He was having a homosexual affair with the high-society Lord Alfred when homosexuality was illegal in Britain. Lord Alfred's father learned about the affair, got angry and called Oscar a Sodomite.
Oscar was extremely offended and no doubt worried about the effect such a comment would have on his reputation and success as a writer, so against good advice he initiated a private prosecution against Lord Alfred's father who was subsequently arrested and charged with criminal libel.
Unfortunately for Oscar, his lover's father had the resources to investigate Oscar's background and past activities. During the course of 3 trials it became clear that Oscar Wilde really was a Sodomite (or homosexual), so he was the one who was jailed.
For the confused, freedom of speech is not the same as freedom of behavior and activity. We are not, and certainly should not, be free to murder anyone, even if he happens to be guilty of committing a capital offense.