The Forced Bid What Privatizing Social Security Would Do to Stock Prices, and Why Recent Developments in the Economics of Market Flows Strengthen the Case Against It

Proposals to privatize Social Security through personal investment accounts rest on the assumption that equity markets will deliver real returns of 6 to 7 percent, exceeding what the current program can pay. This paper examines that claim from actuarial, financial, and fiscal perspectives and finds it fails in each. Actuarially, Social Security is not an investment account but a package of inflation-indexed insurance benefits, retirement, disability, survivor, and family coverage, delivered through a progressive formula; no private portfolio replicates this package at comparable cost. Financially, the paper applies the inelastic markets hypothesis (Gabaix and Koijen, 2021), which holds that a dollar of net equity inflow raises total market capitalization by roughly five dollars, to a 2005-style carve-out diverting approximately $330 billion annually into automatic, price-insensitive equity purchases. Under this framework, valuations rise approximately 28 percent above baseline within a decade, compressing forward returns by nearly one percentage point annually and generating roughly $15 trillion in capital gains accruing predominantly to the top decile of households. Crucially, the classical framework of Diamond and Geanakoplos (2003), in which bond issuance offsets equity flows and prices barely move, reaches the same policy verdict by a different route: the equity risk premium shrinks as risk spreads across the workforce, eliminating the excess return the proposal requires. Both models therefore undermine the projected returns, and neither changes the real economics of retirement, which is funded by future production, not financial claims. Fiscal analysis in the functional finance and Modern Monetary Theory traditions confirms that personal accounts financed by government borrowing create no new national saving. The paper concludes that if broader asset ownership is the goal, the appropriate instrument is a voluntary, low-cost add-on savings vehicle layered atop an intact Social Security system, not a carve-out of the payroll tax. In preparing this paper, the author used an AI assistant (Anthropic's Claude and Perplexity, powered by GPT-5.1) for drafting, editing, and formatting support. All analysis, arguments, and conclusions are the author's own, and all references and figures were verified against primary sources.