Mapping Hate and Extremism: How Brazilian Reddit Communities Spread Toxic Discourse

Pedro Augusto Torres Bento, Yan Aquino, ARTHUR BUZELIN, Pedro Robles Dutenhefner, Arthur Chagas, Victoria Estanislau, Lucas Dayrell, Samira Malaquias, Marcelo Sartori Locatelli, Gisele L. Pappa, Wagner Meira Jr.

Abstract:

Online hate speech endangers minoritized groups and has
been linked to offline harassment and violence (M¨ uller and
Schwarz 2020). Yet the mechanisms by which such toxic
discourse spreads and evolves remain context-dependent. In
this work, we focus on Brazilian Reddit communities to ex-
amine these dynamics at scale, focusing on both banned
and non-banned subreddits. Leveraging over 20 million posts
and comments, we employ two complementary approaches:
Word Embedding Association Test (WEAT) to detect im-
plicit semantic biases, and the Pysentimiento transformer
model to classify hate speech in Portuguese-language con-
tent. Our results reveal that banned subreddits exhibit strong
positive associations with hate-related terminology – partic-
ularly sexism – indicating a normalization of discriminatory
language. In contrast, non-banned communities show broader
but equally concerning patterns of prejudice across multiple
hate categories, such as racism, body shaming, and ideolog-
ical hostility. Additionally, we find evidence of a significant
propagation effect: submissions containing hate speech sub-
stantially increase toxicity in subsequent comment threads.
These findings highlight not only the diverse forms of extrem-
ism manifesting within Brazil’s Reddit ecosystem, but also
critical inconsistencies in content moderation practices. Our
work contributes to a deeper, culturally contextualized under-
standing of online radicalization and offers scalable method-
ologies for monitoring and mitigating toxic discourse on dig-
ital platforms.