Extremism is mostly used in a political or religious sense to refer to an ideology that is considered to be far outside the (acceptable) mainstream attitudes of society. Extremism is a complex phenomenon, although its complexity is often hard to see. Most simply, it can be defined as activities (beliefs, attitudes, feelings, actions, strategies) of a character far removed from the ordinary. In conflict settings it manifests as a severe form of conflict engagement. The threat of extremism is neither constrained by international borders nor limited to any single ideology. Increasingly sophisticated use of the Internet, social media, and information technology by extremists adds an additional layer of complexity. Extremism is very difficult to deal with as it emerges from diverse political, social, economic, and cultural reasons. This study hypothesizes that social identity crisis in South Korea may contribute to emergence of homegrown extremism. Thus, this research analyzed whether five main vulnerable social groups can be influenced by extremism. Categorizing such five groups in South Korea as extremist internet communities, multi-cultural families, ill-treated foreign workers, religious extremists, and school maladjusted students, this study conducted surveys with them. The interview results show that the vulnerable social groups with social identity problems are likely to support or sympathizes extremism.