[Don]

It gave preferential treatment to periodicals, a form of free press, in order to encourage their circulation. The postal laws were content neutral and applied to all periodicals.

Actually, the press is the only commercial industry mentioned in the bill of rights, which guarantees "freedom of the press."
The press is the only commercial interest singled out for special protection in the Constitution. Churches, (freedom of religion) are also singled out, but they're not commercial interests.

The 1st Amendment also expressly protects the right of the people peaceably to assemble.

This refutes the idea that individuals only have rights when acting individually rather than collectively. Churches and the "press" and assembly are examples of individuals acting collectively and those collective activities are expressly protected by the first amendment.