A Survey of Online Hate Speech through the Causal Lens (2021)

Abstract: The societal issue of digital hostility has previously attracted a lot of attention. The topic counts an ample body of literature, yet remains prominent and challenging as ever due to its subjective nature. We posit that a better understanding of this problem will require the use of causal inference frameworks. This survey summarises the relevant research that revolves around estimations of causal effects related to online hate speech. Initially, we provide an argumentation as to why re-establishing the exploration of hate speech in causal terms is of the essence. Following that, we give an overview of the leading studies classified with respect to the direction of their outcomes, as well as an outline of all related research, and a summary of open research problems that can influence future work on the topic.

## introduction user-generated content has flourished with the evolution of social media platforms, and with it there has been an emergence of several social phenomena. some of them can have a positive impact on mental health and eventually prove beneficial for societies; for example, it has been shown that the use of social networks from individuals of advanced age can lead to social benefits as well as have promising cognitive effects @xcite . there is, however, a plethora of societal issues on the digital world which are proliferating in these platforms; such are several types of online misbehaviours. despite the clear interest of the research community to prevent, detect and filter harmful content @xcite @xcite @xcite , the problem is very complex and still far from addressed. for instance, its multifactorial character poses already a large obstacle with manifold parameters to consider: diversity of platforms, abundance of languages, various facets it can manifest on, and different forms of language, to name a few. even at a higher level, there are some deeply philosophical issues to contemplate, such as the thin line between awry, unwelcome content and freedom of speech. nonetheless, the impact of online communications on society is considered more beneficial than harmful, hence it is important to advance the current scientific work to address its limitations. the matter of unhealthy discourse is widely context-dependent @xcite and subjective @xcite . a racial slur, for instance, will be interpreted differently from individuals with separate ethnic or racial backgrounds. conversely, however, most existing approaches operate on the individual post/comment level or aggregate isolated pieces of information -usually of textual nature -and seek simplistic, ostensibly universal, decisions. even though this was a necessary course of action at the beginning, such nuanced task requires higher sophistication. to combat the issue to the core, it is of utmost importance to deeply understand the factors that drive it and determine them in a definite way. an increasingly popular scientific approach to ensure certainty is via the application of causal methods. causality suggests an area of study that is ubiquitous in many parts of modern science @xcite @xcite , among which social sciences @xcite . especially with the development of methodologies to extract causation from observational, instead of experimental, studies, it is now possible to utilise the profusion of web content for the extraction of causal knowledge @xcite @xcite . driven from the necessity of contemplating hate speech from a causal prism, there exists a relevant, yet still narrow, body of literature. in this survey, we attempt to summarise the existing research which analyse phenomena of digital misbehaviours from a causal perspective, quantifying the influence on fundamental sociological outcomes related to harmful language online. in addition, we highlight the important research gaps and make suggestions for future directions. the goal of the present paper is to call attention to the importance of causation in the context of the discussed issue. in addition, it is intended to act as a point of reference for aspiring practitioners in the topic. the rest of the paper revolves around the compilation of relevant publications, first classified based on their focus of sociological impact ( §2) and, subsequently, arranged according to their approach towards salient methodological settings. the latter section ( §3) is organised into several prominent hurdles, which include information regarding how they are treated from the reviewed work and points of discussion about the research gaps. ## sociological causal impact digital profanity is, first and foremost, a sociological phenomenon that affects many aspects of the virtual world. there are some pronounced directions which require thorough examination, such as the consequences of such actions on the affected communities as well as their targets, or the impact of banning policies aiming at fighting against it. moreover, there are several other underlying effects that could get in the spotlight, including the ramifications of interventions or the reasons that drive toxic actors. as a result, it is of paramount importance to examine hate speech in a holistic way and concretely quantify the drivers of these outcomes. however, it is impossible to achieve this task without considering causality, because non-causal inferences can never be conclusive. surprisingly, despite the broad interest of the research community in this topic, very little work has been done on attempting causal links, even on the most prominent tasks related to online hate speech (ohs). in the present survey, we classify fundamental sociological outcomes related to ohs and outline the most distinguished body of literature. the classification results into three major pillars, with respect to the following: in all the of the cases, we can consider the role of hate speech both from the position of a phenomenon which is the result of (potentially) multiple causes, but also from the position of the causal root and study its effects. therefore, in the following sections we review both directions. ## difficulties and causal methods experimentation for the sole purpose of causality is fairly costly and, in this case, can be largely unethical, considering that it would mean deliberate exposure of people to toxic material. as a result, it is crucial to exploit the available methodologies of observational causality, in combination with its intersection with natural language processing. there are, however, several open research problems which lie at the heart of textual causality and thus are inherited by this task. a prominent hurdle, for instance, exists in the conception of the causal diagram, contemplating all the possible covariates and determining their roles. such graphs are domain-specific and can greatly deviate, due to differences introduced by the platforms or niche types of speech. furthermore, there are challenges such as the discovery of effective linguistic representations for the various parts where text can act as a surrogate. in this section we discuss some prevailing difficulties, summarise the route of relevant literature, and finally, provide some suggested directions based on previous studies. ## conclusions the task of hate speech mitigation can never be conclusively accomplished unless the research community seriously speculates about its roots. this would mean a methodological experimentation with the phenomenon, from a causal prism. simply put, it would mean taking a step back from its detection and focusing on scientifically breaking it into its causes. if the causes are known, then any further steps can make meaningful change. practitioners should then be able to take crucial actions towards either its efficient and interpretable detection or, even further, its a priori prevention. by understanding the most prominent and fundamental factors leading to the phenomenon, it is possible to conclusively build on its holistic solution. the present survey is intended to initiate discussions towards this direction. by introducing some of the most relevant studies while simultaneously highlighting several points of interest, we aspire for this paper to work as a point of reference, as much as an inspiration and an open call for further research. to make any definite causal claims it is necessary to have a well defined system, where all influential factors are understood or known. all the existing research, including this survey, can only serve as a prelude to future discussions regarding this ubiquitous issue, which will consequently lead to more sophisticated and generalisable models.