Freedom is the inheritance of every believer. Why would you go back? His allegory of Hagar and Sarah is a wild example of this. He is attempting to contrast law with faith, performance with freedom and to persuade them to life free in Christ's righteousness instead of trying to produce their own. Why would anyone, if given freedom, shoos bondage?
I find Galatians 4:8-9 especially compelling. Not knowing God you served by nature things that were not God. Why return not that you know the true God, but better yet, are known by God? We are naturally wired to be anti-God, or at least to ignore him. How great is it to know God? How much greater is it to know that the God of the universe knows me?
The line, "I have labor pains dear children, until Christ is formed (lit., metamorphosis) in you," is a great summary of pastoral ministry. My job is to labor so that Jesus is formed in believers who are then transformed.