Criticism has room for discussion. Criticism can be destructive and constructive. Ridiculing is never constructive. What does ridiculing yield? What benefit does ridiculing have?
Does most ridiculing, aside from satire, have a benefit? Probably not. But it would be a mistake to make any speech without benefit illegal, especially since it is just so easy for anyone in power to conveniently select people for jailtime when legislation uses such broad words as "ridicule".