How much more, when criminals have killed an innocent man in his own house on his own bed, shouldn’t I hold you responsible for his death and rid the earth of you?”
The human heart and mind are capable of turning most any wrong into a right. Ish-boshet was standing in the way of David’s uncontested reign over Israel, but his assassination was not moral. I can see the temptation, but I know it is wrong. Besides that, given David’s response, perhaps he knew the people would not respect his rule since it had been secured through treacherous means. David perceives that and purges the evil from within his kingdom because he knows that wholeness and stability can not be brought about by force. He has to build his kingdom on righteousness, not on the corpses of those who would oppose him.
Walking In Liberty 