"More man's inhumanity to man has been done in the name of religion than any other cause."
Here is another similar phrase. The only posted source I can find is by:
Bratten, Frances C. . "A letter from Germany". Dickinson Newspaper. Dickinson News. This was from a newspaper clipping quoting Sgt. Richard L. Carpenter's letter home from Germany to his mother. Carpenter is citing a quote from 1929. Date is not on clipping but letter written home "... in January 1955."
Does anyone have a better source?