Under certain circumstances I believe this to be true, drugs will be a net positive (HIV comes to mind). However, we know that in most cases genes are not your destiny, it is the combination of genes and environmental triggers (such as diet, lifestyle, pollution, etc.) that cause disease.

To the extent that we encourage people to believe that their actions are meaningless we actually increase the problem by enabling a feeling of helplessness and despair that causes people to put all their faith into a "cure", whether that be some kind of drug to manage the symptoms or gene therapy. Why bother eating healthy when I can simply take this pill?

We also have a mistaken assumption that drugs are somehow perfect solutions when in many cases the cure is worse than the disease (statins come to mind). Combine known side effects with the fact that the research behind the safety and effectiveness of drugs is distorted by the media, manipulated by the drug companies, and ignored by the doctors and what we have is far from a solution to our problems.

You are right that we don't have a long track record of fixing genes (or curing chronic illness) and this should cause us to be humble about what science and technology can achieve. We must acknowledge the potential of science and technology, and thus push the limits of what we are capable of, while being aware of it's limitations, and behaving accordingly.

Skepticism should not become nihilism, nor should science become a religion.