The driver of population increase, or slowdown, is birth rate. There are many factors that affect birth rate which have been well-documented. Abortions scarcely impact on that at all. If you make abortion illegal, there will be more backstreet abortions. Whether or not abortions are permitted doesn't impact on the overall abortion numbers very much at all. This is a matter of sheer statistics. It's rather difficult to see why this has to be explained to intelligent people.