The Talmud tells how Rabbi Meir had wicked neighbors who caused him harm and much anguish. He prayed to G‑d to wipe them out. When his wife, Bruria, heard him praying this way, she scolded him. (Rabbi Yeshaya Horowitz writes in his classic Shnei Luchot HaBrit that if your wife scolds you, even if she is wrong, you should listen--otherwise she may not scold you when you really are wrong.)
Bruria said, "King David wrote, 'May the sins cease from the earth!' Not the sinners, but the sins!"
So Rabbi Meir changed his prayers and in fact, the sinners eventually reformed their ways.
Our purpose on this earth is to heal and repair, not to vanquish and destroy. Yes, there is evil that must be entirely wiped off the face of the universe. Most of our work, however, is in searching out whatever is good, bringing it out of the background and into the foreground.
Furthermore, when we wish ill on someone, there is always a danger that this negative energy might return to us.
The main thing is that our minds should be focused on the light, not the darkness, on those rare but delightful sparks of good and not the mud in which they are buried. Leave the garbage collecting for others--there are plenty of volunteers.
To quote King David once again, "Turn away from evil and do good, seek out peace and pursue it."
Rabbi Tzvi Freeman for Chabad.org