The main finding of a comprehensive empirical research project on the intersubjective acceptability of the pragma-dialectical discussion rules (Van Eemeren, Garssen & Meuffels, 2009) is that ordinary language users judge discussion moves that are considered fallacious from an argumentation-theoretical perspective as unreasonable. In light of this finding it is remarkable that in everyday argumentative discourse fallacies occur regularly and seem many times not to be noticed by the participants in the discourse. This also goes for the abusive argumentum ad hominem. While abusive ad hominem attacks are judged to be very unreasonable discussion moves when the unreasonableness of clear cases of this fallacy is rated in experiments, in real life this fallacy remains undetected more often than not. In this paper it is argued that this paradox can be explained by analysing abusive ad hominem attacks as a mode of strategic manoeuvring which takes on a reasonable appearance in real life situations when it mimics, as it often does, legitimate critical reactions to authority argumentation. The hypothesis that abusive fallacies are seen as less unreasonable when they are presented as if they are critical questions pertaining to the argument scheme for authority argumentation than when they are clear cases was tested systematically in two experiments. The results of these experiments confirmed the hypothesis.