Not only do we have free speech, we have the Freedom of Assembly.As to your point about unions, PP, etc. - I don't believe it's good for most organizations to have overwhelming power in politics. Too much power harms in a small group of wealthy organizations harms the public.
Freedom of assembly, sometimes used interchangeably with the freedom of association, is the individual right to come together and collectively express, promote, pursue and defend common interests. The right to freedom of association is recognized as a human right, a political freedom and a civil liberty.
Freedom of assembly - Wikipedia, the free encyclopedia
You can not change that in the courts or a simple law.