Wright (2003) suggested that the internet is an effective means to rally like-minded people and mobilize lethal consequences, such as recruiting individuals for terror organizations. which concept in social psychology best explains this trend

This is called group polarization. It's a happening or phenomenon in which people's beliefs in a group tend to become more extreme than their own individual beliefs. If a person's base beliefs tend towards caution, this group belief will be extremely cautious, and if they tend towards recklessness, this new group belief will be extremely reckless. After a group discussion oftentimes someone's beliefs that they've already held will become strengthened, heightened.