I honestly doubt Google has thought of this.

Their modus operandi appears to be (1) launch edgy experimental stuff, (2) forget it exists, (3) be reminded it exists, (4) ruin it by killing it or rewriting it.

I can't shake the feeling that virtually every product decision at Google is made by an engineer.

Is that bad? Or is it just different that what we are used to?

It's potentially idiotic in a context where there are non-engineering concerns at play, such as compliance, law, marketing, PR, etc. It exposes them to massive potential liability.

This. Corner the ad market and then work to eliminate all your competitors? The lawsuit practically writes itself.

What if consumers want it, though? Opt-in?

They don't have anything near a browser monopoly.

Their market share in display advertising would be the entry point. Or phones...The EU is already persuing antitrust action around Android.

Is it antitrust if you leverage your 50% market share in one area to help your monopoly market share in a different area? Because I wouldn't have thought so, and I don't see any way their ad market share helps them push an ad blocker.

The display advertising market share would allow them to weather the storm of an ad blocker, especially if the ad blocker were designed to be friendlier to their ads versus others. Roll it out with aggressive blocking, wait for competitors to die, then relax the rules.

Or they could use the Android entry point. The EU seems to think they have a monopoly there, which would imply a "mobile browser" monopoly.