The effect on the demand for children of falling benefits and rising costs has been augmented by a third set of factors: changes in the costs of birth control. Not every couple have exactly the number of children that they ideally would want if that number could be controlled at zero cost. Some parents have fewer than they would like (because of infertility), but historically there have been many more children born than would have been if birth control were costless and perfect. As a result of technological improvements in contraception, weakening or changing religious views that affect the psychic costs of averting birth, and the legalization of abortion, the costs of averting birth have declined substantially in recent years. Most women come closer now than in the past to having the number of children they ideally would want.