**1. Introduction**

Hatred directed at members of groups due to their origin, race, gender, religion, or sexual orientation is not new, but it has taken on a new dimension in the online world. Online hate involves actions involving the denigration, harassment, exclusion, and advocacy of violence against specific groups on the basis of assigned or selected characteristics (i.e., origin, race, gender, religion, or sexual orientation) through information and communication technologies (ICTs) **[1–3]**. Although research regarding online hate is in its infancy, research on offline discrimination has shown that the consequences of exposure and victimization can be severe and it can promote deviant behavior, social disintegration tendencies, and negative health outcomes (i.e., psychosomatic problems, externalizing behavior problems) **[4,5]**. Therefore, it is important to understand why some adolescents perpetrate online hate. Because not much is known about possible correlates of online hate perpetration, the present study examined the association between being bystanders and perpetrators of online hate, and toxic online disinhibition as a potential moderator of this association. The results might help to deepen the knowledge concerning involvement of adolescents in online hate and how the online environment promotes online hate. The findings might provide information for prevention and intervention efforts to tackle online hate among adolescents, thereby promoting democratic coexistence in a pluralistic society.

There are different roles that adolescents can play in online hate, including being bystanders who observe online hate without being directly involved, being victims directly targeted by online hate material, comments, or posts, and being perpetrators who post, forward, or share harmful or hostile online hate material, comments, or posts [6]. Initial research on prevalence suggests that the most common way to experience online hate is by witnessing these behaviors as bystanders. For example, in a study with Finnish adolescents between 15 and 18 years, 53% had witnessed online hate, 6% had perpetrated online hate, and 23% had been victimized by online hate [1]. A common reaction of bystanders of online hate is taking no action, making a comment disagreeing with the online hate post, reporting it, liking the content, or blocking the post [6]. However, researchers have found that being bystanders and perpetrators of offline and online aggression are related [7–9]. Therefore, it seems assumable that some bystanders of online hate might also perpetrate online hate, which might be explained as follows. First, Social Learning Theory postulates that adolescents who observe deviant behavior and/or perceive that the peer group accepts these behaviors are more likely to engage in similar deviant behavior [10]. In these cases, perpetrating online hate might be explained in light of observational learning, adopting inappropriate coping strategies, and dynamic group processes. The Social Learning Theory has also been expanded to the online context by some researchers that have found that individuals tend to use more aggressive expressions in their online communication and interaction when their peers behave aggressively [11,12]. Second, some adolescents might become desensitized when observing online hate. For instance, initial research has shown that exposure to cyberbullying predicts lower levels of empathic responsiveness [13]. Third, some adolescents might be exposed more often to these behaviors because they are friends with perpetrators and share common values. For example, research on social networks of online and offline bullies has shown evidence for "nests" of cyberbullying perpetrators, assistants, and reinforcers [14,15].

The online environment involves anonymity, invisibility, asynchronicity, textuality, and lack of face-to-face contact, and punishment and repercussions are considered less likely to occur as compared with the offline world [16]. These circumstances can promote rude language, hatred, and threats, also referred to as toxic online disinhibition or the tendency to feel less inhibited [16]. Toxic online disinhibition can also decrease the ability for empathy, self-control, and the ability to recognize social cues [16,17]. When compared to the offline world, there is an increased likelihood that fewer adults are present in the online world of adolescents, which can also increase aggressive behavior and discrimination [18,19]. To the authors' knowledge, no study has investigated the association between toxic online disinhibition and online hate perpetration. However, past research has revealed that higher levels of toxic online disinhibition are positively associated with cyberbullying perpetration, flaming, and trolling [17,20–23]. Therefore, it can be proposed that toxic online disinhibition might also lead to less self-monitoring when expressing beliefs through hateful or degrading writing or speech online, making inappropriate attacks on minorities more likely.

The present study aims to contribute to the existing knowledge about online hate exposure and perpetration among adolescents by focusing on possible moderation effects of toxic online disinhibition in the association between being bystanders and perpetrators of online hate. In contrast to previous research on exposure and perpetration of online aggression, the current study will be the first to investigate these associations among online hate. To guide this purpose, the present study included the following hypotheses:

**Hypothesis 1 (H1).** *Being bystanders of online hate is related positively to being perpetrators of online hate.*

**Hypothesis 2 (H2).** *Higher levels of toxic online disinhibition are positively associated with being perpetrators of online hate.*

**Hypothesis 3 (H3).** *Higher levels of toxic online disinhibition increase the association between being bystanders and being perpetrators of online hate.*
