This assumes that once abortion is illegal every woman with an unplanned pregnancy will place her baby for adoption.  That is clearly not true, given that even the most unwanted pregnancies do not automatically produce unwanted babies.   

This issue also erroneously assumes that the people on waiting lists to adopt would only adopt one child.  If the supply of babies increased, the cost of adoption would go down and most of these people would jump at the chance to adopt more than one child.  Also, the reduced cost of adoption would increase the number of lower and middle income families who could adopt.  Other factors that increase the pool of potential adoptive parents is the growing problem of infertility, and the fact that there is now less stigma attached to single parent adoptions.