Unless you have specific examples that you're thinking of here.
The "don't put this plastic bag on your mouth" warnings come about because the public supports those laws/cases. Those people are at the point were they rely on other to be responsible for them rather than using common sense. Those laws/cases create an environment where people come to expect warnings for everything rather than rely on their own common sense.
I do think you're right that day to life would cause more harm without any warnings, at least for certain people. The people who are responsible for themselves are generally going to be ok in either situation. The people who are happy-go-lucky and rely on others to think for them and arlt high risk in either situation, sometimes regardless of if warnings are present.
The plastic bag warning is aimed at parents of children mostly. Babies, love crinkly things. I know that my son when he started crawling would seek out the on floor garbage cans to play with the bags we used as a liner.
If you have someone who is not thinking about the ramifications, they would let the kid play with the bag, kid would end up putting it over their head(yay, surround sound) and some percentage would die.
There are similar warnings on buckets, about drowning. Kids that age love water, if they manage to get themselves head first in a 5 gallon bucket it only takes an inch of liquid of so for them to drown. Most people wouldn't think it takes so little.
On any given mountain climb, maybe. But overall? I don't know. A coworker of mine who liked mountaineering made lots of acquaintances in that lifestyle, and he told me they are often missing limbs and show lots of ugly scars, and have lots of near-death anecdotes about themselves. I'm talking about people who do this either for a living or as an all-consuming lifestyle, not casuals.
He told me of a girl, a pro mountaineer, who was missing several fingers and had plenty of teeth knocked out. Her skin looked terrible, too. And he told me this is common. Her boyfriend was also a mountaineer, because that's yet another common fact: mountaineers band together, it's difficult to be in a couple with one if you don't find that lifestyle fascinating.
Another friend who does parachuting (from airplanes) told me he knows lots of people who do BASE jumping (or even worse, those senseless "wingsuit" jumpers) and they tend to die young. They do a lot of it, always chasing a more extreme high, until one day they simply don't make it.