United in Hate analyzes the Left's contemporary romance with militant Islam as a continuation of the Left's love affair with communist totalitarianism in the twentieth century. Just as the Left was drawn to the communist killing machines of Lenin, Stalin, Mao, Pol Pot, and Castro, so too it is now attracted to radical Islam.

Both the radical Left and radical Islam possess a profound hatred for Western culture, for a capitalist economic structure that recognizes individual achievement, and for the Judeo-Christian heritage of the United States. Both seek to establish a new world order: leftists in the form of a classless communist society, and Islamists in the form of a caliphate ruled by sharia law. To achieve these goals, both are willing to "wipe the slate clean" by means of limitless carnage, with the ultimate goal of erecting their utopia upon the ruins of the system they have destroyed.