For Christians, Jesus is the image of God. He is the one who shows us what God is actually like. Everything in the Bible, every question we ask, etc should be considered in light of His life & example.
And Jesus's example is a life of sacrifice & love. Love your neighbor as yourself. Do unto others as you would have them do unto you. Love your enemies. Greater love has no one than this, to lay down one's life for their friends. I think these commands do carry some level of subjectivity. It does seem, however, that to harm someone would not be consistent with Jesus's example or teachings, & therefore it could not be from God.