Chris Yiu, technologist at the Tony Blair Institute for Global Change (yes, really) has written a good thread about online advertising and targeting. His view is that it's generally A Good Thing, and there are other, bigger problems to worry about:
This doesn't mean I think the status quo is OK - we could do with a lot more transparency about how ads are being targeted, and there is still room for improvement on making sure people know and have a choice about when their behaviour is being captured, stored and shared.
But the fact of the matter is, there are real products and services where zero is the best price point for everyone because it enables the greatest number of people to participate. And in these cases, carrying ads is often the best way to monetise.