Also nobody mentions that large gathering make easy to spread a propaganda. It is indoctrination. While many people are oblivious to WT doctrines and lag in field service, the convention attempts to stir up the association of one individual to a large pool of people by production of well measured hysteria. In that moment, people became spiritually delirious and feel the moment of being Chosen people. I witnessed several of these conventions where tens of thousands JWs gathered in one place like in Strahov 1991 with 80,000 to 100,000 people, and the mass spiritual hysteria had occurred.
The mass gatherings are not specialty of JWs, they were invented in the 19th century by German nationalists. Mass rallies became popular for other nationals in Austria-Hungary as early as 1868 as a result of Pan-german conventions. Later they had political context and were used by both Stalin and Hitler totalitarian regimes. North Korea also stages mass rallies like this, were people are introduced under strict guideline to the state propaganda. I remember this form of brainwashing from communist rallies in the 80-85, which were extremely similar to the one I attended in Strahov: Enemies (political/spiritual like Satan), better future ahead (classless society/paradise), new goals... etc.