Comment by redwall_hp

The Constitution binds the activity of the government, individuals are irrelevant. Congress is forbidden from passing a law that violates the inalienable rights of humans, freedom of speech and association being one that is conveniently enumerated in the first amendment.

You will not find anywhere in the text that limits this to citizenship (with the sparse examples of the concept of citizenship coming up being things like eligibility for presidential office). The purpose of the Constitution is to spell out the abilities of the government, and one of the things it is expressly forbidden from doing is passing laws that curtail peoples' ability to communicate or associate.