This article, and all research along similar lines (of which there is plenty), also explodes the myth that adoption fixes everything. Many unwanted babies are born after gestation in the inhospitable womb of a mother who doesn't care what effects her drinking, drug-taking, junk-food-eating, partying-all-night-to-deafening-music has on the developing fetus. Much of the resulting damage is irreversible.
Sadly, you make a good point. What you say is, however, an argument for removing children from the custody of such mothers once they are born. One might also use it as an argument to regulate mothers' behaviors--another controversial issue. It is also used by those who favor legal abortion.
Sounds like the womb my husband was in. He was more angry when he found out that his parents planned him...and still his mom drank, smoked, and drugged up when pregnant.