Correct. Good point!
True, you have a right of freedom of speech, but other people have a right to privacy, and a right to their dignity. Freedom of speech is of no merit if it is being used to defame someone with lies. The fact that they are “public figures” is immaterial (Does Sarah Palin have to put up with attempts to besmirch her character?)
Now of course, if what you are saying are lies, then there should be no problem, but unfortunately people believe there is no “smoke without fire”. And how much value should your good name have?
So, if you assert that MJ is a kiddy-fiddler, then you are, frankly, telling a lie, because a court of law has cleared him of that charge. You can say that he was accused of molesting children. You can say that he was arrested and charged with the crime. You can say that you disagree with the verdict. You can even say that MJ got off because of his money and power (very likely), but you cannot say he was a paedophile (actually I think you can now, because I dont believe it is possible to slander or libel a dead person).