The Internet would become leaner, but I can't see how it would not also become better.
That's assuming these people have other jobs (which will have to somehow be funded by something other than ads or selling data -- bye bye 90% of Silicon Valley.) Having other jobs means they won't be able to spend as much time on it and quality will suffer.
> The good content will be kept afloat by donations.
Donations often don't stretch beyond what's required to do the work that's been done before (people don't often donate once the donation goal has been reached.) This stifles growth.
> The usual corporate content will be written off as "marketing expense".
So companies that derive their value from the content they produce and sell ads on have to write off their entire business model as a "marketing expense". Good idea. Say goodbye to virtually all online publishing that isn't paywalled already.
> The ad-supported worthless crap will disappear. You mean like Google, YouTube, Facebook, Spotify, Twitter...?
Three of those provide paid-for tiers. The other two that do not, well...
Optimally.
It plays out optimally.
If everyone suddenly installed and ran an aggressive ad-blocker, we could strangle all of the tracking networks overnight and the Internet would become a noticeably nicer place.
People who refuse to concede that allowing ads is functionally the same thing as inviting third parties to monitor your browsing patterns and invade your privacy are being disingenuous.
How would the horse merchants operate if everyone used cars?
How would window fixers survive if there were no stones being thrown?