Yeah I get impatient with the "they need to make money" apologist argument. Oh, I get it, you're saying I should trust them because they're in it for the money like everybody else. Makes sense thanx.
They need money to achieve their mission though: maintaining a browser (in a landscape of evolving security challenges, performance & web standards) and research (e.g. projects like Rust, Servo & pdf.js originated that way) is not cheap. And currently it mostly comes from search engine deals. If they cannot get a similar one, it all collapses.
I can see why they try to diversify their income. That said, I don't agree with the way they do it here.
IMO coding missile software to pay for those projects would be a lot more ethical than what they're doing. Yeah I consider the ad industry and its privacy crushing consequences worse than weapons almost never fired.