We DO recommend that individuals with high risk of injuring themselves wear helmets. People have varying levels of risk tolerance before they take steps to mitigate them; I'm sure some people choose to wear helmets because they estimate the risk of falling to be too high. In your hypothetical, I would probably not care, because to I and to most people the risk of falling at any given moment isn't high enough to warrant mitigating it. On an airplane, your risk of encountering turbulence is markedly high, enough so that it is worth mitigating. If you disagree then feel free to take your belt off, but don't complain if you die a very avoidable death. (Not that you could at that point.)