| DOI:10.1371/P144 web journal.pone.0155923 June 17,16 /Digital Norm Enforcement in Online FirestormsFig 5. Online aggression dependent on intrinsic motivation and anonymity (fixed-effects). Predictions of Table 1, Model 2. doi:10.1371/journal.pone.0155923.gangst about foreign infiltration by hate speeches against migrants. Norm enforcers punish actors of public interest who cause negative externalities for society or their sub-group by negative word-of-mouth. The technical conditions in social media, such as enhanced visibility and lowered sanctioning costs, have contributed to the expansion of bilateral and multilateral aggressive sanctions which can lead to firestorm-like patterns. Based on this theoretical conceptualization, we also underpinned that online anonymity does not promote online aggression in the context of online firestorms. There are no reasons for anonymity if people want to stand up for higher-order moral principles and if anonymity decreases the effectiveness of sanctions for norm enforcement. By showing this, we hope to make a number of valuable contributions to the field of online aggression in social media. First, online aggression in a social-political online setting is not primarily an illegitimate and irrational behavior, performed by narcissistic and impulsive actors with a lack of empathy, social skills and emotional regulation problems acting out of personal revenge (such as in [5, 13]). Online aggression in social media resembles a practice of sousveillance [98]: it accomodates a growing digital civil society that actively uses the available masses of weak ties in social media to publicly enforce social-political norms. Social norm theory offers a theoretical foundation for research on online aggression, which up to now has been largely driven by the absence of theory or psychological interpretations of traditional bullying theory (for example [15]). Second, it is one of the first studies that has investigated the role of anonymity for online aggression in a social-political online setting by relying on a large dataset that is representative of the proposed digital civil society, i.e., commenters who actively contribute to a wide range of social-political norm enforcement (see also [73]). Third, we challengedPLOS ONE | DOI:10.1371/journal.pone.0155923 June 17,17 /Digital Norm Enforcement in Online FirestormsFig 6. Online aggression dependent on anonymity of commenters (random-effects). Predictions of Table 1, Model 1. doi:10.1371/journal.pone.0155923.gthe popular claim that negative word-of-mouth in social media is mainly PD98059 web caused by commenters’ anonymity. In contrast, the results support the idea that non-anonymous aggressive sanctions are more effective. Non-anonymity helps to gain recognition [78], increases one’s persuasive power [74], and mobilizes followers [85]. The result is also in line with public voices that observe an increasing social acceptance of non-anonymous digital hate speeches [99]. This study also has practical implications. First, it can be expected that in the future, digital norm enforcement will intensify. The growing digital civil society adapts to the digital environment that transforms interactions. Social media offer great opportunities for individuals who have the intrinsic desire to enforce norms and contribute to the formation of latent interest groups. Second, the regularly demanded abolition of online anonymity and the introduction of real-name policies do not necessarily prevent onl.| DOI:10.1371/journal.pone.0155923 June 17,16 /Digital Norm Enforcement in Online FirestormsFig 5. Online aggression dependent on intrinsic motivation and anonymity (fixed-effects). Predictions of Table 1, Model 2. doi:10.1371/journal.pone.0155923.gangst about foreign infiltration by hate speeches against migrants. Norm enforcers punish actors of public interest who cause negative externalities for society or their sub-group by negative word-of-mouth. The technical conditions in social media, such as enhanced visibility and lowered sanctioning costs, have contributed to the expansion of bilateral and multilateral aggressive sanctions which can lead to firestorm-like patterns. Based on this theoretical conceptualization, we also underpinned that online anonymity does not promote online aggression in the context of online firestorms. There are no reasons for anonymity if people want to stand up for higher-order moral principles and if anonymity decreases the effectiveness of sanctions for norm enforcement. By showing this, we hope to make a number of valuable contributions to the field of online aggression in social media. First, online aggression in a social-political online setting is not primarily an illegitimate and irrational behavior, performed by narcissistic and impulsive actors with a lack of empathy, social skills and emotional regulation problems acting out of personal revenge (such as in [5, 13]). Online aggression in social media resembles a practice of sousveillance [98]: it accomodates a growing digital civil society that actively uses the available masses of weak ties in social media to publicly enforce social-political norms. Social norm theory offers a theoretical foundation for research on online aggression, which up to now has been largely driven by the absence of theory or psychological interpretations of traditional bullying theory (for example [15]). Second, it is one of the first studies that has investigated the role of anonymity for online aggression in a social-political online setting by relying on a large dataset that is representative of the proposed digital civil society, i.e., commenters who actively contribute to a wide range of social-political norm enforcement (see also [73]). Third, we challengedPLOS ONE | DOI:10.1371/journal.pone.0155923 June 17,17 /Digital Norm Enforcement in Online FirestormsFig 6. Online aggression dependent on anonymity of commenters (random-effects). Predictions of Table 1, Model 1. doi:10.1371/journal.pone.0155923.gthe popular claim that negative word-of-mouth in social media is mainly caused by commenters’ anonymity. In contrast, the results support the idea that non-anonymous aggressive sanctions are more effective. Non-anonymity helps to gain recognition [78], increases one’s persuasive power [74], and mobilizes followers [85]. The result is also in line with public voices that observe an increasing social acceptance of non-anonymous digital hate speeches [99]. This study also has practical implications. First, it can be expected that in the future, digital norm enforcement will intensify. The growing digital civil society adapts to the digital environment that transforms interactions. Social media offer great opportunities for individuals who have the intrinsic desire to enforce norms and contribute to the formation of latent interest groups. Second, the regularly demanded abolition of online anonymity and the introduction of real-name policies do not necessarily prevent onl.