Can John Stuart Mill’s radicalism achieve liberal egalitarian ends? Joseph Persky’s The Political Economy of Progress is a provocative and compelling discussion of Mill’s economic thought. It is also a defense of radical political economy. Providing valuable historical context, Persky traces Mill’s intellectual journey as an outspoken proponent of laissez-faire to a cautious supporter of co-operative socialism. I propose two problems with Persky’s optimistic take on radical social reform. First, demands for substantive equality have led past radicals to endorse exclusionary nationalist and eugenics policies. It pushes some contemporary radicals towards illiberal interventions into intimate social life. Second, the radical critique of capitalism relies on an account of profit that neglects the epistemic function of private-property markets. Once this is acknowledged, capitalism retains some progressive credentials against radical alternatives.