MacGuire and friends had a small army of unemployed World War I veterans training in the California desert. When Butler understood what was really going on, he called J. Edgar Hoover, tipped him off, and a small army of FBI agents raided the camp and carried off the weapons. Nobody was arrested.
I wonder why not?
Oliver Stone indeed. The MacGuire incident is interesting, but the article seems to try to piece together various anti-New Deal elements into a conspiracy that does remind me of the film JFK, or, even worse, Michael Moore's bilge. The New Masses, from which the author draws heavily, was an organ of the Communist Party, rather than simply a "leftist magazine," and it became standard practice for the magazine to play up a large, corporate-oriented fascist movement spreading its tentacles across the country in hopes of recruiting leftists into the CP. Al Smith did have a falling out with Roosevelt following the 1928 election, but the American Liberty League hardly was a subversive organization. Sure, the departure from the gold standard angered a lot of people--both conservative Republicans and elements of the old progressive wing of the Democratic Party. This hardly rises to the level of a coup d'etat, though.
A more simple explanation of the "silence" of the mass media on MacGuire was that the incident simply did not warrant that much coverage. Ickes's book on the press was but one of many works that appeared in the period bemoaning the corporate consolidation of the newspaper industry. Roosevelt had friends in the media, but he also had his opponents, too. Interesting stuff, yes. A bit overblown? I think so.