Hate speech is a major problem, especially in the political environment, where it generates polarization and social conflict. There are no experimental laboratory studies that have analyzed the mechanisms of action of hate speech using biometric records to evaluate the implicit negative emotion caused by these discourses, despite the essential importance of emotion in this problem. This work investigates the interaction between the ideology of the source and the audience (progressive vs. conservative) and the type of message (hate vs. non-hate) on cognitions (perception of the veracity of the message and the source) and negative emotion (biometric and self-reported). Biometric emotion was assessed by recording heart rate variability and electrodermal response. The results highlight the importance of evaluating implicit biometric responses that reveal inaccessible data with other methodologies: conservatives show more emotion in their biometric records than in self-reported ones. With these measures, hate desensitization effects are also detected in both audiences. With self-reported measures, more negative emotion is detected in progressive audiences only when the source is contrary to their ideology; on the other hand, conservatives show less negative emotion in all cases. These results are interpreted as a consequence of normative pressure and endogroup cognitive biases.