It's not the case that advertisers will get the same results, they just won't be able to see/attribute them. Rather, ad platform targeting will be far worse without attribution, and so advertisers won't be able to invest as much in ads while getting the same ROI.
Surely 99% of people don't realise that 3rd parties can scrape which groups they're in/pages they're fans of? The scraper doesn't even need to add them as a friend for this, provided the group/page isn't private.