In the developed world where men and women can both have a career you find parents who really want a boy and parents who really want a girl. It's less about "we need a boy so he can marry a girl and bring wealth into our family and take care of us when we're older" since women are not treated as chattel. As both boys and girls are considered important and equal partners in marriage both support each other's parents when they are older.
So in the developed world this won't lead to gender imbalance. However, gender selection is a very bad idea for some countries, particularly China. Maybe if they repeal their one child policy there won't be an imbalance. The policy is actually not good for China. It is leading in the long term to an aging population without enough of a working age base to take care of them. A 2 child policy would've been wiser, but birth control, education, and enabling parents to put their kids up for adoption (they don't allow this which is why so many kids wind up abandoned on the streets!) would've lead to better results and no child limit would've been necessary. The policy is even worse given that it punishes the poor. Rich families can afford fines and reduced social benefits and have as many kids as they want.
Not only can gender selection be sound, it will further advance our genetic knowledge and insure a bright future.
First of all, I believe that gender selection should only be used after parents have had a single child and would like to have a baby of the opposite sex or would like to select two children of the opposite sex. This policy would ensure that gender selection would not create an unbalanced number of males and females.
Secondly, procedures similar gender selection can be created to alter an embryo's genes in a positive way. Altering genes can decrease risks of future sickness and disabilities and completely prevent inherited illnesses in the baby and will reduce the risk of it occurring in future generations. We can accomplish this feat by starting as small as just choosing X or Y chromosomes.
In conclusion, gender selection is wonderful when used properly and parents can have the boy or girl that they dreamed. By doing this, they contribute to genetic research which will one day lead us to a brighter future with fewer medical problems for the world to worry about.
It is not culturally sound to allow for gender selection. The most obvious reason is that if everyone selected one particular sex then human kind would end in one generation. Another reason is that once we begin to mess with the reproduction in any way, we will then try to manipulate looks, height, intelligence. It leads to bad things.
Pre-selecting genders of children will lead to a gender inequality similar to the current problems in China because of their one child law. Laws like China's will lead to an unnatural ration of boys to girls. In China today, many men have no prospect of finding a partner because they outnumber women by the millions.