The Club of Rome took “too many people” to be more than one billion. Beyond that would risk mass rebellion, world anarchy (we seem on the tip of it now):
A keen and anxious awareness is evolving to suggest that fundamental changes will have to take place in the world order and its power structures, in the distribution of wealth and income.
(The Club of Rome’s view is quoted from page 157 of Energy and Climate Wars: How naive politicians, green ideologues, and media elites are undermining the truth about energy and climate, by Peter C. Glover and Michael J. Economies. Continuum, 2010)