How about instead of telling people to have more kids or less kids, we let them do whatever they feel like?
Not saying that having more or fewer or no kids is going to have a negative impact. But if it was important for humanity to encourage more or fewer or no kids, I think it's pretty natural that there would be campaigns (funded by governments and NGOs alike) to push people in the direction that was supposed to be better.
That's pretty much the entire purpose of any kind of public policy. In theory, anyway.