The bottom line seems to always be salvation - is a person 'saved'. We are obsessed with this question to the distortion of the gospel, the church, the kingdom, and spirituality. We look at the world in terms of who's in and who's out. We create an exclusive mindset foreign to God as displayed in Jesus.
I suggest a new question that will help us see the world correctly: 'is this person loved?'
Now everyone is 'in' and I ought to treat them as such. Everyone is loved, and I am to help everyone discover how to live in that divine love by discipling them. When Jesus was seeking and saving the lost was he looking for outsiders to bring on the inside, or was he seeking and redirecting those who'd wandered away from God - but who were still God's children?
Our sinful actions make us enemies and aliens to God, but God is no alien and enemy to us. He is always the loving Father, close and caring. The prodigal stopped being a son to his father, but the father never stopped being father to the boy.
From the son's perspective, he was on the 'outs' with his father, but such was not the case from the father's perspective. His son was always 'in' even though the older brother never understood it. The lesson isn't just for the older son to acknowledge the return of the younger, but to develop the kind of love the father always had for the prodigal. The father's love for the prodigal never saw him as having lost his place in the family, just his way of living in harmony as part of the family. We are the superior-feeling older brother when we banish the prodigal from the family because he's foolishly lost his way.
We do no wrong if we consider all the world 'in' by virtue of God's love. Not only are we not approving of sin, we find ourselves in a better posture by virtue of love and acceptance from which to make disciples of all nations.