An open web means I can host whatever (legal content) I want on my website and people are free to view it or not view it if they find it undesirable. Current ad blockers play well into this scheme because they protect the end user's right to view content in the way that they want.
This move by Google on the other hand is telling websites that they have to play by Google's content rules or have their website broken by default.
I'm not sure that's the web that I want to live in.