Those activities aren't perceived as risky. They are to some extent, though probably not as much as riding a bike on high-traffic roads (with or without a helmet). Most people drive their car every day and will never get in a serious accident. Every frequent bike rider will hit their head on pavement a few times.
But again, it's all perception. Driving without a seat belt is considered similarly stupid. The reason is that the cost of wearing a seat belt (like the cost of wearing a helmet) is trivial and the benefits are (or at least would seem to be) significant.
The last thing you mentioned is something entirely different, called altruism. That's shown in many animals, and is a case of choosing replication of a gene over survival. It's entirely unrelated, and it also occurs a hell of a lot more in movies than it does in real life.
But again, it's all perception. Driving without a seat belt is considered similarly stupid. The reason is that the cost of wearing a seat belt (like the cost of wearing a helmet) is trivial and the benefits are (or at least would seem to be) significant.
The last thing you mentioned is something entirely different, called altruism. That's shown in many animals, and is a case of choosing replication of a gene over survival. It's entirely unrelated, and it also occurs a hell of a lot more in movies than it does in real life.