The issue is that shrinking the population over a short period of time (and I mean more than 10% a generation) means that you have a lack of young people to take care of older people. And that's ignoring all the capitalism issues that come with all this.

Not every young person is willing to spend the majority of their free time taking care of their parents. Hell, most people aren't willing to do that more than once or twice a week, yet once you get past 70, a lot people need constant care. That's the original point of elderly homes. Of course, those homes are just plain shit and closer to cruel and unusual torture than actually a form of care (especially here in Ontario). And that's not to mention that occupancy is so tight that there's a wait list on them.

Then there's the fact that if our population drops too quickly, we'll have massive holes in essential services as well. There's already a massive hole in all blue-collar work as it stands as people would rather go into the service industry than skilled labour. And while pay is an issue, this is a problem in the States as well, where pay is far better. It's to the point that they've legalized child labour in several places just to make up for the shortfall.

Population decline is an easy way to destroy society, even ignoring capitalist needs.