Sin is transgression of God’s Law. It’s the Bible word for lying, stealing, lusting, hatred, murder, adultery, etc. So I have a problem with your assertion that atheists don’t lie, steal or lust. I have spoken to thousands of atheists and I don’t recall even one of them saying that he hadn’t broken some, if not all of the Commandments. If you disagree, take the test. Go through each of the Commandments (with a tender conscience) listed on www.NeedGod.com and see how you do.