Let's avoid the religious debate and assume Evolution is real
The prime drivers of evolution are
1) Random gene mutations
2) Survival of the Fittest/Natural Selection
The issue I see is that humans actively fight against natural selection/survival of the fittest...
We have hospitals where we treat down's syndrome, cancer, epilepsy, and all forms of mental and physical retardation
Without intervention, these "bad genes" would die and leave the gene pool... but, we keep these people alive, to pass on "bad genes" to the next generation
I know it sounds callous, etc., but it seems like a stupid idea to fill the gene pool with "bad genes", rather than let nature take it's course and kill off the poor bastards who drew the short straw
If a dog breeder had a dog with an obvious deformity, it would not use the dog for breeding purposes... that would be stupid to contaminate the breed's gene pool
I will not argue with the theory of evolution and with the principle of the survival of the fittest. We are existing on this planet because our dna is the result of constant adoption and adjustment to the environment. But lets proceed to the bad genes you are talking off. Its not actually a problem of bad genes but the problem on not exposing the right medicines and exact therapy to cure diseases. For example the sickness called cancer, the cure was already found out long ago but it was not hidden by the medical society and the reason is the multi-billion profit from treating cancer.