But decreasing population is quite feasible and cheap. But now it is possible to control fertility using technology and economic incentives. A long run no growth target requires a major change in mind-set for economics. The logistic curve, the normal population growth pattern observed in biology, is not much used in economics. The scarcity assumption is no longer inevitable in a world with birth control pills.
Societies can collectively choose abundance by limiting population.
Feminist economists have proposed assumptions of abundance and caring for others to replace the conventional individualistic Hobbsian view. By accepting global resource limits and therefore the necessity for population and consumption limits, we can address the poverty problem in a way offering reasonable hope for good outcomes. The above is, admittedly, a sermon that may offends some peoples' faith.