'Cursing' in the Bible

Then Abishai, the son of Zeruiah, said to the king, Is this dead dog to go on cursing my lord the king? let me go over and take off his head.

And the king said, What have I to do with you, you sons of Zeruiah? Let him go on cursing, for the Lord has said, Put a curse on David, and who then may say, Why have you done so?

And David said to Abishai and to all his servants, You see how my son, the offspring of my body, has made designs against my life: how much more then may this Benjamite do so? Let him be, and let him go on cursing; for the Lord has given him orders.

It may be that the Lord will take note of my wrongs, and give me back good in answer to his cursing of me today.

So David and his men went on their way: and Shimei went by the hillside parallel with them, cursing and sending stones and dust at him.

But Abishai, the son of Zeruiah, said, Is not death the right fate for Shimei, because he has been cursing the one marked by the holy oil?