It's a cheap and convenient excuse. Even if Sinkies were breeding like rabbits in an alternate timeline, the shameless PAP regime would be shilling for a 12, 13 or 15 million population. The goal posts would shift with a switch in narrative.
The truth is that totalitarian regimes can only build, demolish and rebuild infrastructure to sustainably grow the economy. And infrastructure is worthless if there are not enough warm bodies to utilize them and provide the ROI.