The “new paternalism” claims that careful policy interventions can help people make better decisions in terms of their own welfare, with only mild or nonexistent infringement of personal autonomy and choice. This claim to moderation is not sustainable. Applying the insights of the modern literature on slippery slopes to new paternalist policies suggests that such policies are particularly vulnerable to expansion. This is true even if policymakers are fully rational. More importantly, the slippery-slope potential is especially great if policymakers are not fully rational, but instead share the behavioral and cognitive biases attributed to the people their policies are supposed to help. Accepting the new paternalist approach creates a risk of accepting, in the long run, greater restrictions on individual autonomy than have been heretofore acknowledged.