>Useful inventions don't need advertising to spread.

This is a common superstition, like faeries or psychic powers.

>Are we really happier than hunters and gatherers

Are you talking about the people who had like a 40% murder rate? The people with piles of dead babies buried out back.

The modern world is depressing and frought with new problems, but most of them are the inevitable product of high population density. Many of our inventions are built to deal with higher population density. The choices are A) create technology with some downsides, or B) genocide

I really don't think I can convince someone that advertising is sometimes necessary when they'd rather smear blood on their forehead and beat a deer to death with a rock.