I think you're also confusing multiple malicious activities occurring on the web. Data harvesting is another thing that needs to be banned into oblivion. Rarely are sites doing that natively. It is being done as a second part of service the site wants. A site/app wants naturally wants to seen analytics about how visitors are using the site/app, so they include some third party tool that provides that data to an extent at the cost of collecting/keeping that data for their own use. Want to make it easy for users to interact with social platforms regarding your site/app, they now get to collect/keep that data. That's a different thing than being served malicious ads.
"I'll pay you if you run this software on your visitors' computers without asking questions" is not a "service" you sign up for. People don't pay you as a service. That's about as shady a deal as it sounds.
It's fully possible to individually negotiate with someone that wants to publish an ad on your site. If you choose to take money from literally anyone who wants to do so, then why would you not be accountable when they inevitably use you to target users for fraud? You chose to take their money and not even look at what you were publishing.