One of the first topics I heard Rabbi Kahane speak about was about the two types of mercy; mercy which is just, and the mercy of fools. There are several Judaic stories that elaborate on this concept. One is about a shepard who rescues a baby wolf. His boss told him, "are you crazy? kill it, but soon, or else there will be trouble with the sheep." The shephard did not listen and nursed the wolf instead. When the wolf grew up, of course he killed some of the sheep.
I think America and especially Israel has made this mistake time and time again. The best most recent example is the 2006 war farce in Lebanon. Israel had mercy upon those "civilians" who were hiding the hezbollah nazis, and did not finish the job.
What was the outcome? The same as always. "He who has mercy upon the cruel, will someday be cruel onto the merciful."