I believe that the most important idea is that life without gravity is not as good as you may think. I believe this because even though you can do things you can't on earth, it has some effect on your body. Most of the excerpt is about how it affects you, and here is some proof: "If astronauts don't force themselves to exercise, their muscles become so feeble that when they return to Earth they can't even walk." As you can see, the author thinks that microgravity is bad, but there are a few sentences where he says it is a fun thing. So I believe that the main idea is that microgravity is fun, but can have terrible affects on your body.
