There are plenty of issues. From economical to non-economical. One big misconception is that shrinking population decreases the use of resources, while some studies showed the opposite is true.

And yes, there are definite issues with overpopulation, but going to the other extreme is not a solution, just another bad decision waiting to happen from people that have no expertise in that area.

There is an interesting conference on the topic that had experts looking at positive and negative aspects of depopulation. You can check it out here.