One thing I think it’s important to remember is that “mercy” doesn’t always come in the form of sunshine and rainbows. I understand the argument that we need more mercy (can’t argue with that), but I think we shouldn’t lose sight of the fact that sometimes mercy can look harsh. To quote myself: “Sometimes mercy doesn’t look or sound like your mom when you scraped your knee when you were 4.”
Jesus often sounded very harsh didn’t He: “Get behind me Satan!” Making a whip and driving people out of the temple? Was He being merciful here? Of course, He was: “All the ways of the Lord are mercy and truth.”
Purgatory is merciful, one of God’s greatest mercies, allowing us to be purified completely before seeing Him as He is. It’s merciful, but it hurts like Hell (literally). But it is what we need.
So, yes, we are always called to be more merciful, and to pray for guidance in how to apply that mercy. We hope it will always be sunshine and light, but sometimes, sometimes the medicine is bitter, a burning coal to the lips and soul of the sinner.