I've used this analogy before, but think of dangerous driving as an analogy for sling tackles. Not many of us go out onto the roads with the intention of driving unsafely or injuring someone. But from time to time, either through carelessness, reckless disregard, or bad technique, people do dumb things on the roads - like run a red light, or overtake in a bad spot.
If you hurt someone doing those things then you will get a severe penalty. Sure you could say 'people run red lights all the time and don't get penalised' or 'if the other person had a better car they wouldn't have been so badly injured', but it misses the point. You can't put everyone in gaol for running a red light, and you can't let people who run a red light and hurt someone get off scot-free as if no-one was impacted.
In life, consequences matter. Sure, it's unlucky sometimes, but that's how life goes. You shouldn't put yourself in the position to hurt someone and get in trouble, but if you do, and no-one gets hurt, you should thank your lucky stars.
Nyhius knocked out a bloke for 45 seconds and he couldn't finish the match. Sure, he played the next week - some people bounce back in a few days, and some take a few weeks. Some get so many knocks they never really bounce back. Some, suffering from CTE, are never the same person. At the extremes, some take their own lives.
If a tackle is careless and someone is knocked out, someone is going to be rubbed out. If the person gets up and plays on, there probably won't be a penalty. You might as well make peace with it, because I can't see it changing any time soon, andI'm not sure it should.