system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is a population decline in a country considered a bad thing?
gpt
The problem, especially with extreme population decline, is that eventually you have too many retired/elderly folks and too few workers to support them.  Either directly supporting elderly parents, or paying into social security.

A slight decline may be fine, but many social systems are set up on the premise of constant population growth.  The same thing can happen even without a population decline if you have a very large generation (such as the baby boomers) who will all retire as a group.