What is required for gun safety is common sense. If someone doesn't have that, a safety class won't help.
I see what you're saying and I hear it often but I'll rebut.
Enough perfectly "smart" people with good "common sense" don't grasp all the nuances of gun safety. "Hey, it's unloaded," is a perfectly logical, common sense thing to say. It isn't acceptable. It isn't safe enough. It gets people killed.
The idea of layering safety measures -- which is why we have four rules when any one of them is capable of saving a life -- is not perfectly intuitive. This is a construct we as a society of shooters have developed over many years. "Common sense" doesn't give you that.
There's also a strong element of group-think, peer influence, that will shape a shooter's habits -- for better or worse. And if someone has not had some figure with authority above that of the current peer group lay down the law about firearms safety, then there's almost no way that group, or any individual in it, is going to rise above bad, dangerous habits. As they say, "None of us is as dumb as all of us."
If you bought a gun, read the instruction manual, never got safety training and you've shot for 42 years and never endangered anyone, never violated any of the 4 rules, never had a moment that could have ended badly, well, that's great! Hats off to you. You're a rare one. There's no way on earth I'd recommend your example as a good course of action for a new shooter.
Yeah, if you've come up in a shooting family, or you learned to shoot in the military, or you started right off joining a competitive shooting discipline with plenty of good peer mentors around, maybe you don't need to take a safety class. Maybe. (There's plenty and way more than plenty examples of all folks from all of those backgrounds who exhibit terrible habits.) Expecting people to be able to figure out and properly apply the safety rules out in the real world, from what they picked up reading the instruction manual of their new .22 would be .... well, a bit part of the problem we see at our shooting clubs and ranges these days.