It is ugly and harsh on the eyes. There's nothing wrong with a minimal no-frills aesthetic, but that doesn't have to mean literally ripping _all_ styling out.
Hundreds of years of typography, typesetting... and what do some people claim to want? Naked html, default styling like a friggin' typewriter! Ugh!
Then you get the best of both worlds!
99.999% of people don't want to design their own custom CSS for every website they visit, though. And the people who do could set custom stylesheets on any site they like. Nothing really needs to change in that regard, the best of both worlds is already here.
Additionally, If every site worked this way, you'd only have to set the stylesheet once.
What you're suggesting might make a nice browser plugin, though. Stylish but with an integrated marketplace.
> majority of people view the complexity of modern design on the web as an extension of design in magazines...
There's a reason for styling. It makes things more legible, aesthetically pleasing and more fully expresses the intent of the content creator. We have different fonts and layouts for the same reason that buildings vary in design and materials. All buildings could be made of cinderblock and in the shape of rectangles but they're not, why do you think that is?
The good thing is that Firefox still has option to override all fonts and use a single one chosen by the user. What is missing though is option to limit font weight to 400 and more.
At the moment I simply don't use websites that use thin fonts. Also websites that abuse fonts to display non-standard (non-unicode) icons fail utterly with user selected font families.
Other than that, having single font family everywhere is much more pleasant.