Yeah it's a good point, and opens up a question. What determines the disciplinary response: the action, the consequence, or both?
It would be a rare case, but it's possible to shoulder barge someone and for them to fall and do serious damage eg a neck injury. However shoulder barges are normally considered a physical but fair way to contest a 50/50 ball.
Likewise, a physical challenge on Chris Morgan may not affect him much, but the same tackle on David Brooks could do considerable harm given his physique.
In all cases the player could take an action that on 99% of occasions would be waved away, do they deserve to be punished for the same action if it happens to result in a serious injury?
We could change the rules to rule out even that 1%, we could make football a non-contact sport and prevent many fouls and injuries but it would then cease to be the same sport.
I dont have any answers i just think these are interesting things to think about