Actualy the problem with Kastner was not really that he was a Zionist but rather that he was an accomplice to mass-murder as was basically proven in a court off law and transcribed in full by the the secular zionist BEn HEcht in his book Perfidy.
So Satmar quite understandbly does not glorify a man that was for the most part a murderer who did one thing to “try and allow people to ignore his entire “resume” that so happened to save the Stmar Rebbe’s life.