Libel or slander? Where has that happened?
Is it libel if someone writes that they don't believe your Prophet? Is it slander if someone says that they don't believe Jesus was the son of God? I think it is pure hyperbole to call making fun of someones beliefs slander or libel.
If you are so concerned about libel and slander then why do you not care if someone starts a thread lying about Judaism? (Oh, that's right, it's only Jews and they deserve it....)
Freedom is a two way street. You have the freedom to say whatever you want about Judaism, and other people have the right to say whatever they want about Islam... or Christianity, or any other religion.