There's no need for an organization to be immune from censure or regulation when its constituents are all themselves immune.
I think this requires some clarification. Obviously it's important that the government can't pass laws preventing people from engaging in collective speech. If two people get together and publish a birth control pamphlet (or a right-to-life pamphlet) the government shouldn't be able to say, "By the terms defined in Statute 778-B, you two are a Filth Advocacy Organization and thereby forbidden from advocating birth control." However, a corporation is voluntarily and explicitly incorporated in order to gain certain privileges from the government, so restricting the speech of corporations doesn't present the same threat to free speech.
I think this requires some clarification. Obviously it's important that the government can't pass laws preventing people from engaging in collective speech. If two people get together and publish a birth control pamphlet (or a right-to-life pamphlet) the government shouldn't be able to say, "By the terms defined in Statute 778-B, you two are a Filth Advocacy Organization and thereby forbidden from advocating birth control." However, a corporation is voluntarily and explicitly incorporated in order to gain certain privileges from the government, so restricting the speech of corporations doesn't present the same threat to free speech.