Matthew 7:18 A good tree cannot bear bad fruit, nor can a bad tree bear good fruit.
I know we can all do bad things and we can all do good things, but bad people seem to inherently side with bad things and vice versa.
This does not mean Christians are always good either. God created us good in the beginning and we chose to do bad things.
When we get back into a good relationship with Christ we do tend to change and turn away from bad ways.
When we live with The Holy Spirit in our lives we will tend to follow His ways more often than not as He continues to guide us.