The reason this freedom is referred to as “the” freedom of speech is to reflect the belief of the Framers that the right to speak freely is pre-political. Stated differently, the freedom of speech is an integral aspect of our humanity. The government does not grant the freedom of speech; it is prohibited from interfering with it.
This is known as a negative right, in the sense that government is negated from interfering with a personal natural right. A natural right is one whose exercise does not require a government permission slip. Speech is the classic example.
The first duty of government is to preserve life, liberty, and property. It is a strange and dangerous government that stifles freedom for some fleeting private purpose. It is equally strange that a freedom-loving people would tolerate this.
The whole purpose of the First Amendment and its underlying values is to encourage open, wide, robust, unbridled debate about the policies and the personnel of the government.