I don't understand why people get so hung up on the fairness of handball penalties? Sometimes penalties are unfortunate and weren't intended by the defender.
I played for a shipping league club in Cork a few years ago. I hadn't played in a while so it took me a few months of hard training to get my fitness up before the manager started including me in a few squads. Eventually I made my debut when he put me on at right back for the night last 20 minutes.
I'd never played full back and as a typically left side attacker, I was well out of my depth. Less than 2 minutes in, I got twisted inside out by one of their forwards, lost him completely and stepped backwards to find him only for the slippery bastard to go over my outstretched leg for a stonewall penalty.
It was unfortunate and certainly unintentional (I didn't know where the fecker was) but even my own mother couldn't have argued it wasn't a pen.
Kimpembe had time to see the shot coming, he had time to turn his body to block it, he had time to lift his arms from his sides to make himself a bigger obstacle between the ball and the goal. This argument that he didn't intend to handball it, or couldn't have know the ball was going to strike his arm is completely irrelevant - the onus is on him not to have his arm in a position away from his body where it could be struck. It's not on the referee to somehow prove his intent.