Intention shouldn't play any role in this. From the moment you make such a dangerous challenge, you should be given the red card + heavy suspension, regardless of whether you injure someone or not.
You just can't separate intention from result in this case. If you make such a challenge, you only have one intention: hurting the player, since there is no way you're going to get the ball. It would be entirely different had there actually been a chance for Witsel to get the ball.
I do agree with you 100% though when you say a heavy suspension is necessary for all such tackles, regardless of whether the victim is (severely) hurt.
Then again, what exactly is a heavy suspension? It might be something completely different for you than it is for me.