Hostility has a trivial effect on persuasiveness of rebutting science denialism on social media.

Polarised social media debates between science deniers and advocates for science frequently devolve into hostilities. We conducted four preregistered experiments (N = 3226; U.S. Americans) to assess how hostility influences the impact of misinformation from science deniers and rebuttals from advocates in social media discussions about vaccination (Experiment 1-3) and genetically modified food (Experiment 4). Results revealed only trivial to small effects of hostility on the persuasiveness of discussants: most internal meta-analyses revealed that the effects of hostility were smaller than the smallest effect size of interest (SESOI: d = 0.2). Thus, rebuttal is effective in mitigating the impact of misinformation on attitudes towards behaviours dismissed by deniers (for example, vaccination) and intentions to perform these behaviours, even if advocates for science lose their temper. Not responding had negative effects. Likewise, misinformation was impactful even if presented in a hostile tone. Hostility, however, consistently reduced the perceived competence of messages.