I participated in publishing the first biography of the Lubavitcher Rebbe as a youth. I too heard the lies Haaretz publishes about the Rebbe's brothers. So, I invested in a few long distance telephone calls to people who knew them personally. One brother, Israel Aryeh Leib, was a brilliant Orthodox mathematician who was not in any way secular. The other brother, Dovber, was placed in a mental hospital by the KGB, a punishment common for people who did not comply with the KGB's wishes. Actually, he was an astute Torah scholar. Although he had a quiet unassuming personality, Dovber was very outgoing at times and aggressive. He was hardly the type of person typically institutionalized.
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from the article: One brother became secular, the other was mentally ill