Sin is harmful, wrong behavior that people cause to each other and so to themselves.
We care about it, because God loves us, and so he want for us only the good. We have to listen and obey him, throughout Bible his word. Like a children to beloved parents.
These verses
"You heard that it was said: ‘You must love your neighbor and hate your enemy.’ However, I say to you: Continue to love your enemies and to pray for those who persecute you,"
"He who is not against us, is for us".
Sounds diverse and humanist to me. But he's talking about someone performing miracles. Can somebody with no affection to him do them?
"He who is not with me is against me".
Sounds like he wants to gather his followers.
I think If creation happened on it's own, we should see unusual breaking of laws of physics in our universe. These would be "new creations" happening by chance, or some other universes entering from the outside, or parts of creation happening one way, some the other way.