Well there's this also thing known as "satire", you know.
Anyway, maybe in the US there are no limits to satire, but I am sure most of the rest of the world has limits to satire. Ridiculing the premier of a nation in such a manner does not in any way aid to the strength of face of that nation to the rest of the world. Just look at how the ridiculousness of the Trump satire makes a joke out of the US system. Just saying...
More downvotes in 3, 2, 1 ....
ALSO, TO YOUR POINT: Who is the judge of what is satire and what is fake news? If Donald Trump called Obama an illegal immigrant today, or better still a wiretapper, is that satire or false accusation? Could he possibly eventually defend himself saying it was satire, his own type albeit? This whole satire thing is a slippery slope. It must have limits.
But do you see how dangerous that would be to make illegal, and how it applies to "ridiculing" as well?
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".