The Soviet Union was an atheist country. Religion was not fully banned there, but religious propaganda was. Since evangelicals believed in Christ's Great Commission, they preached the gospel and many of them were arrested and judged. In addition, many evangelical groups did not have official registration which was also illegal. Most people did not have their own copies of the Bible. It was very hard to get any evangelical theological education. Evangelicals in the Soviet Union almost did not have contacts with evangelicals in other countries. This was a very hard time for evangelicals. However, in my opinion, in these circumstances, it was very easy for evangelical groups to become fanatic.
Below is a video of lawsuit against three leaders (presbyter and two preachers) of a Pentecostal group (Assemblies of God) which took place in 1961. This video was made as a typical communist and atheist propaganda. Unfortunately, it is in Russian and no translation is available.
This video is full of communist and atheist rhetorics. One of the accusations against the Pentecostal leaders was that their literature (in Russian) was printed in the USA. In the Soviet Union, it was a serious thing because everyone who had any contacts with Western people was suspected to be a spy. I am absolutely against arresting and imprisoning people because of their religion.
However, there are two points in this video that cause me mixed feelings. One of them is a story of a woman who joined this group. Before she joined it, she was diagnosed with cancer in initial stage. In this video, it is stated that she could be cured if she had proper medical treatment. However, this group discouraged people from going to doctors. She did not have a treatment and died. Another thing is that it is stated there that one of the preachers refused to serve in the Soviet Army. Since military service was mandatory, he was convicted. These two stories seem to indicate that this group was too fanatic because as far as I know visiting doctors and military service are not against Assemblies of God teachings.
In addition, it seems that this group was not registered because their meetings were secret. They lasted many hours and sometimes from evening until morning. In the video, it is stated that this group recruited people who had difficult periods in life and young people.
It is well known that in the Soviet Union there were some thought reform techniques used. I think this group also used some thought reform techniques. What is better: to be under atheist thought reform or under religious thought reform? I do not know.