It is not just some Christians who feel the moral dubiousness of joy and celebration at the death of evildoers. Here is Rabbi Shmuel Herzfeld. "So our tradition is clear: Public rejoicing about the death of an enemy is entirely inappropriate." Here is a delightfully equivocal statement by Rabbi Tzvi Freeman.
Interestingly, Dennis Prager is still pounding on this theme. About twenty minutes ago I heard him repeat his argument against me and others. The argument could be put like this:
1. The Israelites rejoiced when the Red Sea closed around the Egyptians, drowning them. (Exodus 15)
2. This rejoicing was pleasing to God.
3. To rejoice over the death of evildoers is morally permissible.
This argument is only as good as its second premise. Two questions. First, does the Bible depict God as being pleased at the rejoicing? Not unequivocally. Prager could argue from Ex 15: 22-25 that God was indeed pleased because he showed Moses a tree with which he rendered the bitter waters of Marah sweet and potable. The Israelites were mighty thirsty after three days of traipsing around in the wilderness of Shur after emerging from the Red Sea. Unfortunately, Prager provided no support for (2).
But more important is the second question. Why should we take the fact that God is depicted as being pleased at the rejoicing -- if it is a fact -- as evidence that God is pleased? I grant that if God is pleased at some behavior then that behavior is morally acceptable. But the fact that God is depicted as being pleased does not entail that God is pleased.
And so, as a philosopher, I cannot credit the (1)-(3) argument. It assumes that the Bible is the inerrant word of God. But this is not to be assumed; this is to be tested. The Bible has to satisfy reason's criteria before it can be accepted as true. If the Bible violates the deliverances of practical reason (as it quite clearly does in the Abraham and Isaac story, see my Kant on Abraham and Isaac) then it cannot be accepted in those passages in which the violation occurs as the word of God.
We who have one foot in Athens and the other in Jerusalem face the problem of how we can avoid being torn asunder. On the one hand, philosophy can bring us to the realization that we need revelation; on the other hand, nothing can count as genuine revelation unless it passes muster by reason's own theoretical and practical lights. This is not to demand that the content of revelation be derivable from reason; it is to demand that nothing that purports to be revelation can be credited as genuine revelation if it violates the clearest principles of theoretical and practical reason, for example, the Law of Non-Contradiction and the principles that one may not kill the innocent or rejoice over another man's evil fate.
The problem is to reconcile divine authority with human reason and autonomy. Two nonsolutions may be immediately dismissed: fideism which denigrates reason, and rationalism which denigrates faith.