Is it better to treat the symptoms of a disease over a long period of time or is it better to prevent it?

I recently heard a statistic. A guy said that more drugs and treatments than ever are available for diabetes in the U.S., yet the rate of diabetes in the U.S. has doubled in the past 30 years. So this leaves an important question. What's more important- treating the symptoms of a disease over a long period of time or trying to prevent the disease altogether (if it can possibly be prevented)? Because, if you really think about it, the pharmaceutical industry would make a lot less money if people made efforts to change their lifestyle with a healthy diet and an exercise program. I do realize many diseases are simply genetic; there is no way of avoiding that. If everyone in your family has died of heart disease, there is probably somewhat of a chance of you developing heart disease. But I guess what I am asking deals more with preventative maintenance. What's your view on this?