So once an accusation of antisemitism is made, it is provisionally to be assumed as justified, and anyone who expresses doubt as to its validity is provisionally to be accused of antisemitism, and anyone who expresses doubt as to the validity of that accusation.... And so on ad Infinatum?

That would be particularly unfortunate in a context where it is seriously claimed that it is "antisemitic" to favour the same kind of boycott of Israel that helped change South Africa for the better.