Really is a waste of time in my opinion. Despite appearances from the media, if someone in the US does not want to see firearms in their life, it is very very unlikely that they will ever see firearms (besides police officers') and even more unlikely that they would see a loose one that they should pick up to clear.
It's advice on par with telling someone to set aside money in their retirement for a nuclear bunker.
I think your analogy oversteps -- it's really more akin to teaching people how to use a fire extinguisher, even though they're unlikely to ever encounter a fire.
According to the ATF[1], there are more firearms in America than people. The idea that you might live your whole life and never see one is far from a given, though rurality vs. urbanality almost certainly affects this, as well as the carry laws in the area you live. The statement is almost certainly more true in somewhere like California than it is in Alaska, but in my experience, definitely doesn't hold true for "America" on the whole.
I was going to use CPR as an example. How many people have been trained in CPR vs. those who have actually used it?
That said, the strength of my recommendation is not very strong, but if you're asking, "Why should I take a pistol class?", general safety is a good reason.
It's advice on par with telling someone to set aside money in their retirement for a nuclear bunker.