In this paper, we discuss the fundamental problem generated by social capital in social stratification research from the viewpoint of equality of opportunity. After reviewing the research developments in the field of social stratification, which have been brought about by social capital, we discuss the fundamental problem affecting the relationship between the labor market and social structure. In functionalist terminology, social capital is essentially paradoxical (good and evil) with regard to equality of opportunity (in other words, efficient functioning of labor market). Research on stratification shall accept this paradox and develop theory of equality of opportunity mediated by social relations. In order to represent an analysis framework, for example, we conducted a thought experiment: if we assume that a society's labor market completely depends on social capital, then we can describe the original condition of equality of opportunity and how it was stratified. This framework could serve as a guide for conducting a comparative study from the viewpoint of stratification culture. By analyzing the 2005 Social Stratification and Social Mobility (SSM) Survey data collected in Japan, Korea, and Taiwan, we can reveal that friends' capital and relatives' capital do not necessarily reduce the level of equality of opportunity. Moreover, the mobility pattern in a hypothetical society could have the power to generate a certain volume of the white-collar strata, even if the strength of the same differs among the three countries.