I strongly feel we should strive to decrease the amount of people on this planet: less people means less resources needed to feed and to house them. It means less pressure on the planet's ecosystems, less CO2 produced, less pollution.
The only ethical way to get to a lower amount of people is to have less children. We should see falling birth rates as a good thing, not a problem to be solved.
Are falling birth rates a problem for the economy, as the article hints? I can see how that's a problem, but if the economy only works well when the earth's population is ever increasing, that's clearly not sustainable. The future needs to be sustainable, or human kind is not going to have a future.
Anyone who's ever lived in a place (at a city, province, or national level) whose population is dwindling knows exactly why. Opportunities are fewer and people are generally less wealthy[0].
[0]: I mean real wealth, like living in a comfortable home and being able to afford hobbies. Not your 401k balance.