So you don't understand what dangerous means?
If every time you crossed the road there was a good chance of getting hit by a car something drastic would have to change. That is dangerous. But you don't frequently get hit by a car but there is still a chance of it happening. So the choices are make drastic changes, use different methods like pedestrian crossings or accept the risk.
And this is where the cost comes into it. You wouldn't put pedestrian crossings on every road. You put them where they are needed the most. But it doesn't eliminate all risk.