The 'gay' gene--I've not researched that one in any kind of detail, but I know there's evidence both for/against. I think the jury's still out, however.
Selective breeding is a form of genetic manipulation--genetic manipulation just allows us to narrow it down to a specific gene.
We need to do years' worth more research on humans before we start messing with our genetic structure, however. For instance, it would seem to be desirable to get rid of sickle cell anemia by getting rid of the gene that causes it. However, being a carrier of the sickle cell gene on just one of the pair of chromosomes doesn't cause the disease (sickle cell disease is autosomal recessive, meaning you have to have the bad gene on both of that pair of chromosomes to get the disease), but being a carrier does give some protection against malaria. We'd have to be very careful that we're not getting rid of some incidental benefits that might come with being a carrier of a bad gene. I don't think you'll get too much argument for getting rid of the bad genes that cause Tay-Sachs or breast cancer, however.
We'd have to be very careful to set up some ethics standards, but there'll still be those who will find and pay someone unscrupulous enough to mess with genes for non-medical purposes.