More pointedly how much harm is caused by not giving them individuated and appropriate but also real independence? Skills take time and practice to develop. What would you expect to result from a failure to actively and persistently develop the independence that a child will require for the rest of their life?
The same dynamic has come up with COVID. There is known harm through infection but also through isolation. In my family we are extremely conservative and careful (probably overly, privileged-ly, and wastefully so) but we ensure regular playdates with a small set of children with careful parents so that our young child can still develop friendships and social skills. And, you know, be a kid. Taking a year off that, particularly at the current age of my child would be extremely harmful so we spend all of our risk chits on that.
Similarly, while never doing anything would reduce many active risks studies have shown being sedentary is more deadly than smoking.
A cost to benefit maximization process is almost always appropriate.
I too was given autonomy when growing up, and I credit it to giving me comparatively far better life skills than my peers. I walked home and cooked myself lunch since the 4th grade. I did my own laundry. I spent untold hours in the park. It taught me how to look after myself and make critical judgements, skills that I watched some friends learn and develop in university 10 years after me. The stress of which can lead to drastically worse decisions when you're 20+ than when you're 10.
Sure we don't outlaw cars, but it's reasonable to minimize unnecessary risk while cars are a necessity in most urban areas.
More importantly, there are greater dangers in the form of accidents. Kids aren't careful, they might run across the street where a driver has trouble seeing them. They might touch a down wire. There's a lot that could happen when you don't keep an eye on kids.