Re: "...grandmother was the secretary if the New York Communist Party..."
In the 1930's many intellectuals and truth-seeking individuals were attracted to Communism, believing it promised an end to war, an end to unemployment, recession, and depression, and seeing in its literature and propaganda a "scientific" system of political order which would end divisions based on class and race.
When Stalin signed his Treaty with Nazi Germany, and rumors of purges, torture, slave labor, and concentration camps inside "The Workers' Paradise" began reaching the West, the majority of American Communist Party members began to become disillusioned and feel that they had been deceived.
Only when considering the actual socio-economic & political realities of the U.S. and the rest of the world during the 1920's & 1930's is it possible to understand Communism's appeal.
Much of the status quo we take for granted today, did not exist during those days. The Communist Party was the first and only political movement calling for equal rights among races and women's full rights, and it was the only voice denouncing Colonialism and Imperialism by the Western powers and denouncing Anti-Semitism (throughout the U.S. Jews were forbidden access to higher education, certain professions, and even access to hotels and motels...signs would be hung right out in the open reading things such as "NO JEWS OR DOGS ALLOWED"...the few universities which would accept Jews had a "Jew quota" limiting admittance to only a handful of applicants.)
In light of what I've described above (just the tip of the iceberg) it becomes more understandable why a brand new philosophy and political order which promised "pie in the sky" to each and all would be found attractive to many young people back in that time.
With all we know of Communism today, with its history of enslavement, murder, genocide, and totalitarian rule, membership in "The Party" seems unforgivable.