You can block third-party advertising structurally, so that a content-cop isn't required. First-party advertising cannot be blocked, of course, since that's just content.

For example, using browsers that impose a Content Security Policy that prevents anything from being loaded from domains other than the origin.

Sure, but if the only ad restriction was mandatory blocking of third party content, you'd just see ad agencies work out ways they can get the content they want to serve hosted locally (and lots of more interesting third party embedded content cease to exist due to it not having the same commercial rationale for workarounds...). If you start forcing companies not to promote third party products with anything that even looks like an ad, you'll just see a greater proportion of the free-to-access internet turn into paid-for reviews and influencer marketing. Not sure that'd be an improvement, and I'm pretty sure the next logical step of getting the content cops ruling which content looks too commercially-oriented for us proles to look at is even worse.

You can block third party advertising structurally using uBlock without ruining the internet for everyone else.

Advertising isn't a thoughtcrime, it's a cognitive/psychological assault.

I think a combination of consumer protection laws, truth in advertising laws and data protection laws, all turned up to 11 (even GDPR), could achieve most of the desired outcome on the Internet without much problematic "content-policing". But I'm not sure. You won't eliminate advertising from the Internet entirely, but making it illegal would make undesirable advertising more expensive, by creating vast amount of risk for advertisers and simultaneously destroying the adtech industry, thus rendering most of the abusive practices that much less efficient.

(Also, to be clear, I want all advertising gone. Not just on-line, the meatspace one too.)