Again...you misunderstand Rothbard who was always hatching new strategies to "borrow in" existing movements, left, right, or center. Four years after this letter, Rothbard was supporting Adlai Stevenson, some years after that he was praising the leftist Peace and Freedom movement, eventually he supported Perot, Buchanan and Bush. You need to view this from Rothbards' Machivillian (strategic) mindset. One could have equally imagined him rationalizing support for Henry Wallace in 1948!
Dr. Rothbard's sense of judgement in foreign affairs was often lacking. There was no moral equivalence between the Allies and the Axis in World War II, nor between the Western democracies and the Communist bloc in the Cold War. Even Pat Buchanan understood this. Whatever its flaws, our system is inheriently superior to fascism and communism. Also, Naziism and Communism were agressive ideologies with aspirations to world domination, as is militant Islam today. The USA and her allies were well justified in their opposition. Both Rothbard and his intellectual heirs such as Lew Rockwell and Justin Raimundo do not appear to understand these realities.
My reservations in this area notwithstanding, Rothbard was unusually perceptive in the economic and the domestic political arena. In his letter, written while Richard Nixon was a freshmen Congressman, Kevin Phillips was in grade school, and Ronald Reagan was a New Deal liberal and a labor leader, he anticipated the "Southern strategy" uniting the conservative wing of the Democratic Party with the GOP. Like several other thinkers, such as John T. Flynn, H.L. Mencken, and Robert L. Dabney, Rothbard foresaw the consequences of bad political and cultural decisions on our country.
No man is perfect, including Senator Lott or Dr. Rothbard. Yet his letter, written 53 years ago, perceived the need to develop a coalition to preserve the political concepts of the Founding Fathers. Rothbard deserves credit in this area.