This whole argument about corporate personhood is an enormous distraction.
Corporations have certain rights not because they are legally persons, but because they are formed by and made up of persons.
Here is my simple formulation. Inidividuals have the right to free speech. Individuals have the right to association. It is crazy to then posit that individuals, when they associate, no longer have free speech rights. If five of us gather on a park bench, we have not somehow given up our speech or other rights by doing so. And the fact that we may form a formal club or organization among us with bylaws and hierarchies does not change this fact one bit.
By the way, if the First Amendment does not apply to individuals who have assembled into a corporation, does the Fourth Amendment apply? How about the Fifth? or Sixth? of Seventh? or Eighth?