In fact, even though humankind has achieved a high degree of technological development, evolution goes on. There are always evolutionary pressures acting on the genetic background of every linving organism. The fact that humans possess the means to control many diseases does not make us immune to selection and hence to evolution. The change that did occur is that we incorporated into our environment all the cultural achievements for the past several thousand years. On that complex environment of natural and cultural constraints our genetic background is developing.
Selection is different in every environment and our milieu is simply, a more complex one.
In any case, due to the large size of the human population and its long generation time, evolutionary change is very slow, but it is undoubtedly happening. This led me to the common belief that undesirable traits are always eliminated by natural selection. Sometimes it does but in many other cases these 'undesirable' traits are hidden to selection and then kept in a population genes. That is the case of the mutations that manifest themselves only when present in homozygosis in an individual, but when individuals are heterozygotes there is no deleterious effect on the individual. If there is no difference at all between such an individual and the 'normal' one, selection cannot eliminate it, and the mutated gene can be trasmitted to the next generation.