Justice Brennan (Roberts v. Jaycees, 468 U.S. 609):
Our decisions have referred to constitutionally protected "freedom of association" in two distinct senses. In one line of decisions, the Court has concluded that choices to enter into and maintain certain intimate human relationships must be secured against undue intrusion by the State because of the role of such relationships in safeguarding the individual freedom that is central to our constitutional scheme. In this respect, freedom of association receives protection as a fundamental element of personal liberty (italics mine). In another set of decisions, the Court has recognized the right to associate for the purpose of engaging in those activities protected by the First Amendment-- speech, assembly, petition for the redress of grievances, and the exercise of religion. The Constitution guarantees freedom of association of this kind as an indispensable means of preserving other individual liberties (italics mine).
The intrinsic and instrumental features of constitutionally protected association may, of course, coincide.
This distinction is much forgotten in constitutional analysis today. It is because the so-called instrumental features are tied to much recognized rights enunciated in the letter of the First Amendment itself. But I think, the intrinsic and fundamental right to freedom of association is of much substantive and deeper value...