But Marky, I expalined why I think your proposal is unethical, no matter what country is facing a population problem.
An analogy: Suppose there were a traffic congestion problem. You propose that the government (openly or secretly) install switches on all cars such that 30% of them randomly fail to start on any given day. Doesn’t make much sense does it?
If we want to control fertillity, it makes much more sense to allow people to control their fertillity. And there is ample evidence that if people are allowed to control their own fertillity they tend to chose to have fewer children. Case closed.