They are all fools.Since the lectionary has paired this psalm with the reading about David's mistreatment of Bathsheba and of his loyal general Uriah, we may read it as a commentary on him. Even the king, even the one loved by the Lord, sins.
They behave as if they don't believe that God exists.
None of them do what they should.
Shouldn't they be afraid?
And, this psalm reminds us that David is not the only one who acts as if he doesn't believe in the Lord.
The psalmist cries out, "Don't they see? Aren't they afraid? Don't they realize whose side God is on?" and then reminds us that even if we neglect the poor, the Lord will not. Someday, things will be the way God wants them to be.