Many people who want a child have a preference for a boy or a girl. That's always been the case and there are many folk methods that supposedly influence the sex of the child people will have. The technological ability to do this reliably is growing, but should it be used? Might we upset the balance between males and females?
Females are not being born at an increasing rate. Females have always had a slightly higher survival rate than males. Males are more likely to die in wars, which occur globally all the time. Looking at male/female population charts for the past one hundred years one can clearly make out were the major wars occurred, the effect is that prominent.
More to the point however, females have a huge advantage over males for a vast number of genetic reasons. The one I'd like to point out however is the fact that females have two X chromosomes while males only have one. Any chromosomal disorders located on the X chromosome (X-Linked disorders) will show up in males far more frequently for this reason, and can lead to many difficulties in life and even a natural abortion of the fetus. To explain further, take the example of a father (XY) and mother (XX), the father has a normal X chromosome but the mother has a recessive (a "normal" X chromosome will override the faulty recessive one and give a normal phenotype free of the disorder) mutation on one of her chromosomes.
--X X" Disregard the --, they're there for proper spacing.
X XX XX"
Y XY X"Y
As this punnett square shows, neither female (XX, XX") will have the disorder since they both contain at least one normal X chromosome. For those interested, a more specific answer would state that half the woman's cells would be normal and half mutant since only one X chromosome is used in each cell, but since the disorder is defined as recessive this is unnecessary information. The point here is that due to the male having only one X chromosome, half of the male children will develop the disorder. The XY child is normal, but the X"Y child will show the mutant phenotype. Depending on the mutation this could be quite deleterious, and result in a lower survival rate. Keep in mind that not all mutations are bad however, and our X"Y child may just gain a benefit from it. This is rare however, so globally we see a lower birth rate of males compared to that of females.
In our societies it really doesn't matter that much but there are other places where boys are tools to earn money and girls too but in a different way,I would not like to be a girl nor a boy to be born for that reason,to earn money.
What should we do? We should run a simulation because this is a pretty easy problem to model.
What I believe without evidence is that world population (because that is what we can measure) would be invariant with respect to sex ratios up to a very large imbalance. Think of the vast economic pressure in favor of Octomons if there were too few females. This assumes that we ever get to a point where some significant portion of the population has the option and takes the option.
Remember, 1/2 the population lives below the median wealth level :). They don't live in cities and don't usually get access to much technology. Do you know how many people never make a phone call in their entire life? One guess is 75% or 4.5 billion.
It might mess with monogamous relationships but that is already happening with that pesky phenomena called modernity.
WRT Gattica -- humans have an innate capacity for depression, anxiety, missplaced car keys... Beautiful shiny people would live lives much like our own.