The issue of sustainability is inextricably linked to that of income inequality. In the Laudato si’, Pope Francis states, “[W]e have to realize that a true ecological approach always becomes a social approach; it must integrate questions of justice in debates on the environment, so as to hear both the cry of the earth and the cry of the poor.” As such, Catholic Social Thought (CST) provides a set of principles for the moral evaluation of an economic system, and these principles address sustainability, income inequality, and other concerns such as subsidiarity and universal access. However, these principles are not uniform in their guidance; there is a complex interplay among them. To illustrate how adherence to one principle may compromise adherence to another, we apply a CST lens to the three significant provisions of the U.S. individual tax system: the preferential rate on capital gains, the home mortgage interest deduction, and the exclusion from taxation of employer payments for health insurance. Together, these provisions cost the U.S. budget more than $4 trillion over a ten-year period. While the preferential rate on capital gains can be viewed as consistent with the subsidiarity principle preserving private liberties in choosing investments, this provision is inconsistent the principles related to prioritizing social obligations such as those towards labor. The deduction for home mortgage interest can be claimed as consistent with the universal access principle and the right to private property ownership. However, upon closer examination, the economic outcome of this provision is inconsistent with the principle of equitable distribution of burdens and benefits. Finally, the exclusion from taxation of employer payments for employees’ health insurance prioritizes labor by providing health insurance to workers, but the fact that only employed persons are able to participate in this benefit challenges the principle of meaningful participation for all. Taken together, our constructive criticism of existing tax policy brings to light consequences of the tax system not typically discussed in policy analysis. Our use of a CST framework adds a principles-based perspective to an ongoing and contemporary debate about specific economic policy. Finally, our exploration of the tradeoffs that emerge among CST principles when jointly applied highlights the importance of confronting these tradeoffs in designing and evaluating policies and how they move us closer to or further away from a sustainable economic system that supports integral human development.