Well, it'd be immediately visible to the users. While I think it is blackmail, ABP has a lot to lose by not enforcing strict standards.

They whitelist Taboola, Outbrain, and other native ad networks. I think the strict standards horse has left the barn.

Outbrain provides "uses who read this also read these", no? Or do they also do shady things like splicing in ads between "proper" recommendations?

If ABP started letting unacceptable ads through they'd lose all their users. Enlightened self-interest and all that.

Good point. It only works until somebody decides that they are leaving money on the table.