There have been numerous anti-semites who joined the Birch Society and there is a long history of anti-semitic incidents.  Yes, most of those individuals either resigned or were expelled.  However, as was shown by the internal JBS controversy over John McManus's comments before Catholic organizations, every-so-often anti-semitism does rear its head.

The 1965 California Senate report referred to a "dangerous increase" of anti-semitism within the JBS because of incidents they were aware of.

Nobody is claiming that the JBS is an anti-semitic organization but, sometimes, it has associated itself with (or employed) anti-semites such as Eric Dudley Butler, Gordon (Jack) Mohr, and other individuals, including authors who presented anti-semitic themes or used anti-semitic sources in their writings. The official JBS position on Israel was that it was a Communist-dominated country; Robert Welch described a "zionist conspiracy" that pre-dated and subsumed the Communist conspiracy.