Settling Scores - With God's Approval?

I'm reading 1 Kings.  The first two chapters are about then end of King David's life and the transfer of power to King Solomon.  What strikes me is that the intrigue isn't much different than we see today.  As Ecclesiastes says "ain't nothing new under the sun!" 

 

For example here is King David giving Solomon instructions on how to settle a couple of old scores.  I especially liked the second one where King David says something like 'hey I said I wouldn't kill him but after I'm gone you do what you think is best (hint, hint).'  :)

1 Kings 2:5-9(NKJV)

“Moreover you know also what Joab the son of Zeruiah did to me, and what he did to the two commanders of the armies of Israel, to Abner the son of Ner and Amasa the son of Jether, whom he killed. And he shed the blood of war in peacetime, and put the blood of war on his belt that was around his waist, and on his sandals that were on his feet. 

Therefore do according to your wisdom, and do not let his gray hair go down to the grave in peace.

“But show kindness to the sons of Barzillai the Gileadite, and let them be among those who eat at your table, for so they came to me when I fled from Absalom your brother.

“And see, you have with you Shimei the son of Gera, a Benjamite from Bahurim, who cursed me with a malicious curse in the day when I went to Mahanaim. But he came down to meet me at the Jordan, and I swore to him by the Lord, saying, ‘I will not put you to death with the sword.’ 

Now therefore, do not hold him guiltless, for you are a wise man and know what you ought to do to him; but bring his gray hair down to the grave with blood.”

Then the rest of the chapter tells a couple of stories about how Solomon wacked several of the folks from the old guard who had wronged King David and replaced them with is own people.  Solomon even went so far as to have one guy killed on the alter. 

 

The guy was clinging to the alter thinking it would keep him from being killed.  Solomon gave the guy a chance to come down before they killed him and he refused so Solomon had him killed on the alter.

 

What strikes me about this is that I don't see God disapproving of this anywhere.  And why should he?  These were not innocent men.  They were men who had wronged King David and were now simply reaping the consequences of their actions.  But I'm sure there are people who read 1st Kings 2 and think "it isn't fair".

 

Another way of saying "isn't fair" is "isn't just".  Since I don't see God condemning this anywhere are those people saying that God is unjust?