>Or are you referring to a common interpretation, typically of language that is absent from the Constitution?
Not GP, but there is text that says this -- no interpretation required:
"Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances."[0]
And
"All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the State wherein they reside. No State shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States; nor shall any State deprive any person of life, liberty, or property, without due process of law; nor deny to any person within its jurisdiction the equal protection of the laws. "[1][2]
> Private companies can't violate an individual's First Amendment rights. Only governments can.
Which part of the quoted text supports this claim? Answer: none of it. Interpretation: since it doesn't mention private companies in this context, private companies and the first amendment are not connected, and the former cannot violate someone's rights under the latter. Not an unreasonable interpretation, but not found in the text.
"Congress shall make no law..." And that extended to the states by the 14th Amendment.
Passing a law forcing someone (or a group of "someones", which is what a corporation is) to host/amplify speech they don't wish to host/amplify is "abridging free speech" and is explicitly forbidden by the First Amendment.
The original claim here was a corporation cannot infringe first amendment rights.
That was followed by the claim that this is actually in the Constitution.
But the constitution does not say this. It says (if you go with the corporations-are-people-with-first-amendment-rights interpretation) that the government may not abridge the first amendment rights of corporations (and, usually the accompanying implicit coda, nor the rights of individuals using technology provided by corporations).
> The original claim here was a corporation cannot infringe first amendment rights.
Yes, because the first amendment is explicitly about rights protecting you from the government.
If a law says "the government can't do X to you", then nothing individuals or corporations do can violate that law. Obviously. I'm not sure why this is difficult to grasp.
"Precedent" would imply that this is merely the interpretation of earlier courts, but no, the first amendment is quite explicit about what the rights therein are protecting you from, and it's not private groups.
Or are you referring to a common interpretation, typically of language that is absent from the Constitution?