[foxfluff]

Based on how many trash sites show up in search (even after search engines' algorithms try hard to downrank garbage), I wouldn't be surprised if more than 90% of the web is there only to make a quick buck with ads. According to Wikipedia, 90% of all email traffic in 2014 was spam, despite hosting providers and ISPs blocking ports and taking a hard stance on spam. I have no reason to believe the web is much better, especially given that spinning up a trash site is not going to start alerts and get IP blocks banned the same way that sending email spam does.

I think removing ads' profitability and the incentive to create more trash would be good for the web.

But you're right that with all the trash gone, there's would still be millions and millions of useful sites. The entire web isn't motivated by ad impressions and there are good reasons to run sites with no ads whatsoever.