  Moral Foundations Theory proposes that individuals with conflicting political
views base their behavior on different principles chosen from a small group of
universal moral foundations. This study proposes using a set of widely accepted
moral foundations (Fairness, Ingroup loyalty, Authority, and Purity) as proxies
to determine the degree of radicalization of online communities. The fifth
principle, Care, is generally surpassed by others, which are higher in the
radicalized groups' moral hierarchy. Moreover, the presented data-driven
methodological framework proposes an alternative way to measure whether a
community complies with some moral principle or foundation: not evaluating its
speech, but its behavior through interactions of its individuals, establishing
a bridge between structural features of the interaction network and the
intensity of communities' radicalization regarding the considered moral
foundations. Two foundations may be assessed using the network's structural
characteristics: Ingroup loyalty measured by group-level modularity, and
Authority evaluated using group domination for detecting potential hierarchical
substructures within the network. By analyzing the set of Pareto-optimal groups
regarding a multidimensional moral relevance scale, the most radicalized
communities are identified among those considered extreme in some of their
attitudes or views. The application of the proposed framework is illustrated
using real-world datasets. The radicalized communities' behavior exhibits
increasing isolation, and its authorities and leaders show growing domination
over their audience. There were also detected differences between users'
behavior and speech, showing that individuals tend to share more 'extreme'
ingroup content than that they publish: extreme views get more likes on social
media.
