In many scriptures and stories, sages and saits curse others when they get upset or someone does them wrong. In some cases this can be considered as an act of self-defense (even saits need to protect their material integrity), but in many it seems to be just abusing their mighty powers. One such example could be rishi Durvasa, who appears to get angry at the slightest pretext and shows very little mercy.
This seems very confusing to me, because I always felt the virtues of a sait are compassion, forgiveness and their goal is to relieve the human kind from suffering, not the opposite.
My hyphotesis is that by bringing a curse on a sinner, it acts as a penance and thus the person can get rid of his/her bad karma in this life. But this explains only some of the cases, in many others the action that provoked such a curse is just s tiny mistake, like in the case of king Nriga.