@Bernard
Agree, declining population is a good thing, specially when they occur naturally (like the black death and other plagues) - it tends to kill the poorest and dumbest.

The issue is welfare and government spending - there's a hard limit on how much you can tax your citizens and keep your power, status quo and economic production.
Plus, socialism favors dysgenics as the rich and productive have incentives to have fewer babies and the poor to have even more.