The website is signing up for a service. You could say that a website continuing to use the service of a known malicious ad provider is problematic, but are there any ad providers known to have not served malicious something?

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.