Mercy is a feature of our covenant-making God. However, we do not live in a covenant-making world. Christians have foolishly envisioned God as an overindulgent grandfather. The vision of us, like the Israelites, destroying the covenant we just made with our God-King is entirely missing from that worldview. Instead God skips sin and goes straight to smiling forgiveness. When we don't acknowledge that our sins (even the "little" ones) are an affront to the covenant we made with God, we have no idea that we desperately need his mercy to save us from our deserved punishment.
Secular society has forsaken the idea of covenant in an entirely different way. Unlike Christians who neglect it in favor of God's love, unbelievers often have no acknowledged "law." They make mistakes, explain their dysfunction, or excuse themselves based on personality. With no law giving, covenant making God to sin against, there is no need for mercy at all.
What happens when we neither experience nor acknowledge mercy?
We become merciless.