It would greatly help if Bronco would provide statistics.
First, let's use the term "unintended pregancies" rather than "unwanted". That removes the issue of divining the intent of the mother and rightly places the focus more on the planning aspect.
Second, it is wrong to state that "very, very, few truly unwanted pregnancies that actually become a drain on society". Notwithstanding the mealyness of that sentence (as in, who gets to decide what "truly" is a drain on society?), what data we have refudiates it.
It would behoove Bronco to read this:
Link
Namely, this:
Results: Excluding miscarriages, 49% of the pregnancies concluding in 1994 were unintended; 54% of these ended in abortion.
You can find other reports, and more recent data, by googling the search string "guttmacher institute number of unintended pregancies".
Of course, this doesn't settle how many of those unintended pregnancies are "truly" a drain on society, but then, that is little more than a red herring, I assume, to distract us. No one is able to accurately track and measure what is "truly" a drain on society. For that part, if we're going to use economic factors to base our abortion decision, one need only look at Freakonomics to come to the opposite conclusion (that abortion is an economic plus).
The rest of Bronco's analysis withers away when we use the correct term "unintended" rather than "unwanted".
The problem is the number of unintended pregancies. If you're serious about reducing the number of abortions you have to reduce the number of unintended pregnancies. That is the problem; it is NOT just that poor women are having kids.