Well, I can't do to much about non-Christians and why they do or don't use birth control. Catholics have a rather complex theological view that lends itself to opposition to any birth control, but that same view prevailed within ALL Christian churches until about 1930. Mormon teaching is NOT Christian in any sense of the word, but from what I have read of their own material, theyr believe in the pre-existence of souls and that the faster they can get their wives pregnant, the more of those will be sent to thier homes and thus mor Mormons. This is similar to the baby-souls'-airport you mentioned. However, there is no Christian sect of which I am aware that believes anything like this. Blind adherance to doctrines of church or society is foolish. The Scripture enjoins us to be able to give an answer for our beliefs. This means THINKING -- something that 99% of humanity is loathe to do.
You mistake things when you think that mere population is the cause of poverty. Japan, Singapore, Hong Kong, belie that belief. Mathus was refuted centuries ago, in case you were wondering -- and Paul Erlich has been thoroughly refuted too. Try reading "The Ultimate Resource" by Julian Simon.
There are any number of things God calls a blessing -- a good wife, money, land, cattle, and children. These are blessings in any language or culture.
I'm sure you had these foster kids going off in a van without seatbelts and a leaky exhaust, but what does that do to bolster your contention that large families TEND toward that? This is merely anecdotal evidence. I would say that the very fact that the kids were in foster care in the first place made it unlikely that the parents would be picking them up in a new Beemer. And what solution do you offer? Should you have denied the opportunity to visit with their parents because they didn't have enough money for a car that suited your standards? (It may surprise you to know that most state laws on seatbelts only require belting in as many people as there are belts, but do not require the installation of additional belts.)