You neglect to mention that single motherhood is not only a result of unmarried and unprotected sex, but from deadbeat fathers leaving their children behind when they leave their marriage. I am sure you realize that this is pathetically common and is in no way to be construed as a "choice" made by the mother except for her initial decision to marry a loser.
Even the most amicable divorces with two parents who love the child often result in one parent having physical custody and the other ending up with visitation. This is another scenario for single-parenthood where the custodial parent may not have "chosen" their situation, but rather agreed to it or was ordered by the court to comply.
You are so very right.