You say that criticism can be destructive and constructive, which is true. Ridicule, defined as "[applying] contemptuous and dismissive language or behavior" can swiftly and temptingly become "deconstructive criticism". Or, "criticism that I find humiliating because I don't like it".

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".