Legal Question in Criminal Law in Florida

You may as well ask, why is it illegal to drink and drive while impaired, or to willfully take a human life. Because the legislature says so:

Florida Statute 836.05: Threats; extortion.--Whoever, either verbally or by a written or printed communication, maliciously threatens to accuse another of any crime or offense, or by such communication maliciously threatens an injury to the person, property or reputation of another, or maliciously threatens to expose another to disgrace, or to expose any secret affecting another, or to impute any deformity or lack of chastity to another, with intent thereby to extort money or any pecuniary advantage whatsoever, or with intent to compel the person so threatened, or any other person, to do any act or refrain from doing any act against his or her will, shall be guilty of a felony of the second degree...