Ludwig Von Mises, Crackpot Conspiracy Theorist?

I get this from Sam Tanenhaus' new biography of William F. Buckley, Jr. The index entry for Von Mises is in error.

The John Birch Society was an extreme reactionary organization in the USA. Bob Welch was its leader and founded it near the start of 1959. Welch had a book, The Politician, later known as the Blue Book, that explained what he was about. According to Welch, George Marshall, Dwight Eisenhower, Earl Warren, the Dulles brother, and on and on were all conscious, dedicated Soviet agents.

Buckley had a magazine, National Review. And he was known for trying to show that American conservatives had views worth taking seriously. They are not all crackpots. So he tried to convey an impression that Bob Welch was not welcome in his movement.

The John Birch Society had a monthly magazine, American Opinion. Von Mises was on its board and had articles published in it. I have read quite a bit of Von Mises and about him too, mostly hagiographies. I never met this historical bit before.