Concerns about declining or ageing populations often centre on the fear that fewer people will translate to a weaker economy and lower living standards. But these fears are frequently based on oversimplified or misapplied interpretations of economic models, and appear to be driven more by political agendas rather than evidence. In reality, long-term prosperity depends more on how societies invest in education, skills, and technology, not just how many people they have. We examine national data at the global scale to test whether slower population growth or ageing populations are linked to worse economic or social outcomes. Using nine different indices of socio-economic performance (domestic comprehensive wealth, income equality, research and development expenditure, patent applications, human capital, corruption perception index, freedom, planetary pressure-adjusted Human Development Index, healthy life expectancy at birth), we find no evidence that they are. In fact, we find that countries with low or negative population growth perform better on average for all indicators, and that even within-country time series show that most older and slower-growing populations fare better on average. These findings challenge common assumptions and highlight the need to move beyond fear-based and politically motivated narratives toward a more informed understanding of what truly supports thriving societies.