Yes, some critics of Buchanan are unfair, but this does not mean the charge isn't accurate. The ADL/Commentary criticisms use guilt by association and extrapolation in a dubious way. It is more accurate to say that Buchanan is a fascist with a coded antisemitic subtext.
For a progressive set of criticisms, including links to material from Fairness and Accuracy in Reporting, see:
http://www.publiceye.org/rightist/Buchanan/Buchanan.html
Dennis King and I have criticized ADL for its neoconservative politicization of the charge of antisemitism.
Dennis King and Chip Berlet, "ADLgate," Tikkun magazine, Vol. 8, No. 4, 1993.
Dennis King and Chip Berlet, "The A.D.L. Under Fire: It's Shift to Right Has Led to Scandal," The New York Times, May 28, 1993, p. A29 (Op-Ed).
-Chip