One answer to this question is that there are two entirely separate issues regarding life-threatening hazards: the first relates to personal choice, in which the individual has a right to decide for him/herself how much risk is justified for the sake of certain perceived benefits; the second relates to public policy, in which decisions may affect millions of people without their knowledge or consent. It is not unethical for me to choose to risk my life for what I conceive to be worthwhile, or even for fun (as long as I don't expect anyone else to bear the consequences); but it is unethical for me to subject millions of other people to the same level of risks without their consent.