Everyone seems to be in favor of progress. But "progress" is a funny word. It doesn't necessarily mean that something has become stronger, wiser or better. It simply means changing it from being one thing to another and sometimes it turns out to be worse than before.   Consider medicine, for instance. No one can deny  that medical progress has enriched our lives greatly. Because of medical advancements, we eat better, live easier and are able to take care of ourselves more efficiently. We can cure disease with no more than one injection  or a pill. If we have a serious accident, doctors can put us back together again. If we are born with something defective  , they can repair it. They can ease our pain, replace worn parts and give us children. They can even bring us back from death. These are wonderful achievements, but there is a price we have to pay.    Because medicine has reduced death, the population has been rising steadily, in spite of serious efforts to reduce the rate of population growth. A child born in the United States today has better than a 90% chance of survival . Furthermore, medical advances have ensured that most of those new-born children will live to be seventy years of age or more. The result of this progress is a great population increase that threatens  the quality of life, brought about by progress in the medical profession . This passage implies  that population increase is not   _  .
helpful threatening possible dangerous