Or test for a host of other conditions or characteristics.  We already have the capability of testing for the gay gene in utero.  If Hitler were in charge, we would terminate every-such fetus in order to eliminate homosexuality.  Just think, with DNA testing, all the human characteristics we could eradicate.

Keep in mind though that vaccines are not a good analogy.  Those can introduce other (sometime unintended) pathogens into the population.