Almost none of those are good ideas. Walking alone is an exception; it's
very easy for one momentary lapse to cause death or permanent damage in any of the others.
One of mother's best friends died riding in the back of a pickup truck; car accidents are common, but all that happened in her case was that the road had a pothole, she fell, and happened to hit her head too hard and in the wrong spot.
My girlfriend in college fell on her bike while she was going down a hill and passed over some gravel. Her helmet was destroyed. All she needed was stiches, but if she hadn't been wearing a helmet, she probably would have gotten a concussion.
These are just anecdotes, but the point is that taking a small cost (riding safely in cars; wearing helmets on bikes) is far worth it, because the cost is small, and the benefit in the unlikely case is huge.
It's not illegal where I live to not wear seatbelts in the backseat of a car, but I do anyway. I also use condoms when I have sex, and I wash my hands after going to the bathroom.
There's a big difference between systematically overestimating small risks, and blithely allowing black swans to shit all over your life. I hope you never allow your child to do most of those things, and I hope you never do most of them yourself. The world isn't as scary as the TSA wants us to think, but it can still ruin your life in a heartbeat.