Why can't I just do things in my own way and live a good life as I think best?

Are you separated from God by iniquity?  Any sin or rebellion cuts us off from God.  Iniquity is the desire to do your own thing.

Isaiah 59:2 But your iniquities [Iniquity is the desire to do your own thing.] have separated between you and your God, and your sins have hid his face from you, that he will not hear.

You can see that, without Jesus, you must be separated from God.  God wants fellowship with you, but He will not force Himself on you.  If you love your sin more than you love God, then you will reject Jesus.

You need to understand that sin is falling short of the glory of God. 

1. Are you claiming to have attained to the glory of God?  How would anyone do that without God?
2. And how could anyone approach the Holy God unless God made that person holy?
3. God has one way to make a person holy: Jesus Christ. That is simply reality.