Abortion/religious/science question...?

Well a fetus is alive like any cells in your body. But, kangaroos are marsupials and people aren't. A joey would be like a fetus though, because it can't survive outside the womb/pouch, but a joey is called a joey and not a kangaroo, and a fetus is called a fetus and not a person; otherwise the words joey and fetus wouldn't exist.