Bicycle helmets. Let’s start with that because they’re just so rich for this discussion. First off, the physics. Helmets protect against head injuries because

Bicycle helmets. Let’s start with that because they’re just so rich for this discussion. First off, the physics. Helmets protect against head injuries because they absorb impact. You can die from a head injury if you fall over from standing upright ( king hit knockout deaths ). If you add speed to that equation, the forces are larger ( a bicycle ). If you add more speed ( motorcycles ), the forces are even larger. At any of these situations the forces can be large enough to produce skull or spinal fracture or concussion that leads to cerebral edema and death, or even brain damage. The most effective thing is to minimize your down time after an injury. Why do you want to be learning how to talk again when you could be working again in 3 days? In an identical crash with and without a helmet, the only variable to your cognitive recovery time is the forces your head and neck experience. If wearing a helmet reduces those forces, and it does, then that will shorten your recovery time. I like the way I speak just fine, thank you. Then the parenting. When you send your child out to ride a bike, do you say to them, “Wear a helmet!” thinking to yourself that you don’t want them to get a head injury, or do you say to them, “Hey, it’s your choice to wear a helmet or not, and studies have shown that if I force you to wear a helmet, you’re more likely to not ride your bike ( and be safe, yet possibly obese ), while if I don’t force you to wear a helmet you’ll more likely ride your bike ( and risk head injury, but at least be slender ). So, my dear 7 year old, your call: reversible health problems from possible obesity, or potentially irreversible brain damage, what do you choose today? I’m cool with either.” That kind of laissez-faire-oo-la-la-the-state-cannot-regulate-my-choices attitude is why it works for the state to regulate. Because spreading illogical misinformation that can lead to people being harmed, is wrong. Finally, the fait accompli. The really interesting thing these arguments around helmets show is the very point I’m making : that if something dangerous ( riding without a helmet, taking a vaccine ) actually increases health and wellbeing across the board in aggregate ( greater numbers of cyclists leads to more healthy people, fewer instances of disease lead to smaller spread and mortality ), in other words, if something that is risky, is still relatively less risky than its inverse, then that’s a “good thing”, that societies want to adopt. So if you argue that helmets are mandatory, you’re on the side of the state regulating what is best for the group. If you argue that helmets are illegal ( for the arguments mentioned in these comments ), then you are on the side of the state regulating what is best for the group.