That's why hundreds of millions of smokers, smoked, after all. They carefully weighed up the evidence, using their medical training, avoided the lies from tobacco company advertising, used their "
it's just common sense" know-everything superpower, and - in an almost unprecedented moment of human rational decision making - concluded that smoking was better than non-smoking.
No, it didn't happen that way. People smoked because it was cool, and it was cool because marketing people explicitly made it look cool. "Torches of freedom"[1] was how Edward Bernays set out to get women smoking cigarettes, for one famous example, generic "cool guy with a cigarette" in Hollywood films wasn't put there by accident, for another. And one of the main reasons smoking was pushed out was that second hand smoking gives other people cancer. People bought arsenic wallpaper and arsenic cloth. They did not decide, rationally and in full knowledge of the best available information, that green wallpaper was a better choice than their infant child staying alive. Or do you think they did choose that?
OSHA has no moral basis to override or overrule that human being’s own decisions for their own body.
OSHA's basis comes from the fact that there are many human biases, many con tricks, and many unintuitive risks, collectively learned over decades, which one human cannot rationally learn and consider in a short time. Even if that were all it was - a single human choosing whether they gamble with their health - it might be OK, but this is in the situation where a large and well resourced company has a profit-motive to exploit the humans, to coerce them and mislead them and pressure them, to take such risks without due consideration.
And worse, like the case of second hand smoke - you might be willing to climb a high structure without a safety harness, but your willingness means other people will be compelled to do so - by their employers and by peer pressure. You'll be faster, and your equipment costs will be lower. But you'll be putting other people at risk too - if you fall on a coworker, if you drop something on a bystander, if you slip on the floor in your gripless boots and knock someone else - your choices affect other people.
And society is willing to say "we don't want that. You must wear a harness, so that everyone can wear a harness. You must wear grippy boots, so other people can work safely around you.", without "fearing for your life" being a thing which excludes you from the workforce.
[1] https://en.wikipedia.org/wiki/Torches_of_Freedom