Personally, I use ads as a signal to avoid buying certain products. If the ads are too prominent and omnipresent, it's an indication for me that I would be paying quite a premium on their marketing. But that's just me.
Your channel efficiency unavoidably goes down, which increases your cost of customer acquisition because your other channels cannot pick up all of the slack.
Increasing the cost of customer acquisition is going to be bad for your business. You will either need to reduce costs (by hiring less, for example), or increase your prices.
I think people are misconstruing me here. I'm not saying Google advertising is somehow fundamentally necessary to the economy. I'm just saying that it is straight up incorrect to think that there aren't legitimate downsides to removing their ability to police fraud.
But there are also (potentially huge and beneficial) opportunity costs. We will never see alternative business models which are not viable in the existing ecosystem.
The tracking part isn't necessary for fraud detection not even for conversation tracking. It's only necessary for "personalized ads" aka spying on users.