Is David Too Vindictive?

To me, at least, that can often appear to be the case. Consider, for example, Psalm 35.8-9:
"Let destruction take them by surprise!
Let the net they hid catch them!
Let them fall into destruction!
Then I will rejoice in the Lord
And be happy because of his deliverance."
On the face of it, David seems to be rejoicing in the destruction of his enemies. And, of course, there are countless passages in the Psalms similar to this one.

Notice, however, what David writes a few verses later (vv. 13-15):
"When they were sick, I wore sackcloth,
And refrained from eating food.
(If I am lying, may my prayers go unanswered!)
I mourned for them as I would for a friend or my brother.
I bowed down in sorrow as if I were mourning for my mother.
But when I stumbled, they rejoiced and gathered together;
They gathered together to ambush me.
They tore at me without stopping to rest."
David - long before Jesus exhorted anyone to love his enemies - prayed and fasted for his enemies as though they were his friends. That strikes me as remarkable - and it should give us all pause when we think about David and Old Testament morality in general.