There is no "meaning" of life. What even is the meaning of meaning?
Asking about the "meaning" is reallly just asking: How does this affect ME?
Even asking this question is a demonstration of our species' general lack of appreciation for how outragously improbable our existence is.
Stop worrying about your "special purpose" and start being thankful that you're a winner of the trillion-to-one lottery that lets you sit here and think about these things...
How does this apply to the birth-rate issue? Simple, we need to intelligently manage our population size, which means having many-many less people on the planet...