A prerequisite for representative democracy is for citizens to vote in their own interests, and many scholars have argued that exposure to diverse information helps citizens to determine which candidates or policies will best represent their interests and therefore benefits democracy. Despite a greater availability of information, however, I argue that information consumption pattern is not necessarily more diverse on the Internet than in traditional forms of media. By considering information diversity in two different dimensions, namely vertical (concentration of voices) and horizontal (the range of viewpoints), I show that information is more concentrated (less vertically diverse) and polarized (more horizontally diverse) on the Internet than in newspaper circulation. I propose two hypothesis - quality and cascade hypotheses - to explain this observation. The former, the quality hypothesis, is that online institutions allow people consciously and voluntarily to choose the piece of information with the highest intrinsic quality based on people’s private signals, whereas the latter, the cascade hypothesis, is that the cascading process makes online traffic more concentrated and polarized. Evidence supports the cascade and rejects the quality hypothesis. Based on this evidence, I argue that online institutions produce a trade-off between the lower costs of people’s access to political information and the higher costs of a more concentrated and polarized online information readership. The costs arise not from the mere fact that information becomes more concentrated and polarized, but rather from the underlying mechanisms through which concentration and polarization occur—the cascade hypothesis. This cascading process implies that the risk of elite domination as well as the trade-off between the two central components of deliberative democracy, inclusion and thoughtfulness, may persist in many Internet-mediated forms of deliberation. Taken as a whole, this evidence challenges the notion that a greater variety of political information available on the Internet will necessarily benefit democracy.