Mercy should interrupt unnecessary suffering, not necessary accountability.

There is suffering that serves nothing and suffering that is part of taking responsibility, and mercy belongs to the first. Removing the ongoing pain of shame, isolation, or a consequence that has outlived its purpose is worth doing. Removing the accountability itself just leaves the harm unaddressed and the injured party alone with it.

Where you are inclined to be lenient, ask which kind of suffering you are relieving. Ease the excess and keep the part that is doing real work.