The person who would most likely agree with the statement "A revolution is no picnic. We must eliminate capitalism and imperialism even if thousands have to sacrifice their lives" is Mao Zedong.
Mao Zedong was a Chinese Communist revolutionary who led the Communist Party of China to victory against the nationalist forces in the Chinese Civil War. He believed in the elimination of capitalism and imperialism through revolution, and his leadership resulted in significant social and economic changes in China, albeit at the cost of thousands of lives during the Cultural Revolution.
John F. Kennedy, George Marshall, and Harry Truman were not known for advocating for the elimination of capitalism and imperialism through violent revolution.