I'd be completely ok with intent based advertising - I search for $X you show ads that are related to $X. And I'm ok with measuring what percentage of those who click the ad that converts as well. However, that's not where we are today. The appetite for marketing and advertisement has grown to such a level that companies like Facebook want to know every aspect of your life so they can satisfy that appetite. Clearly a) there's a demand from companies big and small and b) it's working. Companies can still be ethical about it - like why should Facebook track every URL I visit (via the Like button)? Or, why not provide an option to opt-out of targeted ads - I don't like them and I do have friends who like them. I get it but provide an option to opt out.

The general retort I hear is what do you have to hide? Like the only thing that people want to hide are the bad and evil stuff.