2 Samuel 24:3

Why doth my lord? — Even in the eyes of the unscrupulous Joab David’s act was abominable. Joab never gives evidence of being influenced by religious motives, but his natural shrewdness sufficed to show him that David’s act was at variance with the fundamental principle of the national existence. Chronicles adds to Joab’s words, “Why will he be a cause of trespass to Israel?” The strong objection of Joab shows that there was something obviously wrong in the action of David.

And against the captains. — Joab’s objections were sustained by his subordinate officers, and David carried through his sinful act by sheer force of self-will.