Ads can be contextual, served based on the content you view, and Google's own Ad Words does in fact just that, as they serve ads based on your search keywords, and that's their biggest revenue source.
People have issues with user profiling, tracking users to gather their interests, and follow them with ads on certain topics across the web. Which is now illegal to do without explicit opt-in consent in the EU. Google does it too btw, with AdSense.
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> Would you rather they not target you with ads and sell google searches for a nickel each?
This is a false choice.
Also, I already pay for YouTube Premium to avoid YouTube's ads. I would gladly pay for a subscription that stopped ads in Google's Search too.
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> Google's ad service literally couldn't check my gmail account against google fi accounts (apparently).
That's irrelevant.
The danger isn't in Google serving you with more relevant ads, the danger is in that data being collected in the first place, linked to your persona.
And contrary to what other HNers say, no, we don't need to wait for a fascist regime in the US to see the dangers of doing that.
China is targeting political activists and they can coerce any company operating within their borders. Being gay or an atheist already puts your life in danger in many parts of this world. Etc.
But OK, say you don't live in those countries. How about the story of that father finding out his daughter is pregnant from the ads being served [1]. And what would you say if your credit score dropped due to your Facebook activity? Or your insurance prices were affected by those who you befriend online?
There are some real, contemporary consequences of user profiling that go beyond Google knowing if you already own a google fi or not ;-)
[1] https://techland.time.com/2012/02/17/how-target-knew-a-high-...