The lie of the statement in the title is obvious to anybody how have met a Jew, or even have seen a picture (which by now would include most of the worlds population).

By some sources the claim arose in early middle ages, due to some canonical way of depicturing profets in the church paintings (some of them were drawn with a crescent on their heads, which were easily mistaken for horns).

While initially born of ignorance, the lie is very dangerous, as it clearly dehumanize Jews and their descendents.

In the modern days an appellation “sons of pigs and monkeys” used for Jews in many muslim communities is a close cousin to the old lie and, while usually whitewashed as not being literally meant, does encourage view of Jews as being deficient humans.

Even more common is this lie in application to the state of Israel when it is called a Nazi or apartheid state. People who use this appellation often claim it to be a part of legitimate critic of Israel policies. In reality, this is going far beyond the bounds of normal political criticism and is not applied to similar behavior in other states. One can compare those “critics” to a man who yells to a woman in a short dress “prostitute” and loudly encourage others to rape her, while excusing own behavior as a legitimate criticism of her choice of the dress.