Throughout time, all species on Earth have evolved in some way. A factor in that evolution is gravity, expecially with land mammals. We have evolved to function with Earths gravity. Gravity affects how we grow and without it weird things start happening.
Without gravity we would be immensely weaker. With less pressure on us our muscles would be much weaker. Bones also wouldn't grow as "correctly" as they do now. All of this would probably lead to shorter lifetimes as well.
Even astronauts today who stay up in space for extended periods of time have minor problems that start appearing. Not as severe as the ones previously mentioned but still. So obviously getting to space is one thing, but this proves that staying there is something else. I would be extremely happy to just go to space so I'm not complaining, its just a concern of mine.