People who join an interest group because of expressive benefits likely joined to express an ideological or moral value that they believe in, such as free speech, civil rights, economic justice, or political equality.
People likely joined to express an ideological or moral value that they believe in civil rights. This was such as free speech. People likely joined to express an ideological or moral value that they believe in economic justice. This was such as free speech. People likely joined to express an ideological or moral value that they believe in political equality. This was such as free speech. These People join an interest group because of expressive benefits.