> that's a real thing advertisers DO want
I think GP is talking about a more specific thing, and it's one I experience all the time too: that I'll visit a website briefly one time, by accident, or to satisfy some curiosity, or look up the specifications on something I already own, or to get a link to send to a friend, or whatever other non-purchase reason, and then get shown ads for their thing over and over and over again until the end of time despite the fact that there's a 0% chance that I will ever buy it.
I'm sure it's true that, in the general case, advertisers want to show ads to customers multiple times, but in these particular cases, they shouldn't want to show them to me -- I'm definitely not going to buy the thing, and they're wasting their money, and it seems like Facebook ought to be able to better differentiate between users like me who will definitely not convert and users who might (like GP said: seems like there ought to be detectable patterns in the way I do or don't engage with the content that should signal my lack of interest).