Well, broadly speaking, I guess it is a personal choice.  Some parents just can't wait to find out whether their little angel is going to be a boy or a girl.  One can understand that feeling.  However, I think it is much better to wait and find out the natural way.  Some might put forth the argument that if the technology exists, why not use it?  They might say why be in the dark when you can find out in a jiffy.  Well, I just think the anticipation of finding out the natural way is a wonderful thing.  You can have the cute arguments/wagers with your spouse about whether it is going to be a boy or a girl, just the whole anticipation thing.

On the other hand, knowing the sex of your child beforehand helps you plan for the child.  You could decorate the room in a particular way, if you knew.  Of course, relatives and friends would want to buy specific gifts for your child, based on whether it would be a girl or a boy.  In that sense, it helps if you know the sex of your child prior to birth.  One could make the argument that it helps provide for the child better.

However, in certain countries, especially Asian ones, knowing the sex of a child before birth can lead to female infanticide, if the fetus turns out to be female.  This unfortunately occurs since in certain Asian cultures boys are valued more than girls, especially since boys are viewed to be providers for the family and girls are viewed as a "burden," since when they marry, they no longer reside with the family and provide for it.

Consequently, girls are discriminated against.  So, sadly, in such countries, knowing the sex of a child beforehand can lead to the abortion of the female fetus.  In such cases, parents should compulsorily not be given the choice to know the sex of the child before birth.  This would be a case of misuse of information.  Therefore, one cannot have a universal view of for or against on this matter.

In normal circumstances, however, it should be a personal choice and it should be up to the parents to decide whether they would want to know the sex of the baby.