alt Hacker NewsDon't get hung up on this specific example of the dating ad.
There's a difference between awareness campaigns and click / conversion campaigns and if there's some ads for a garden chair and your friend is sitting on it you'll definitely remember it more than some random model. Or clothes that are advertised on your body. Not saying that's the future we want, but it would definitely work for a while.
That doesn't come across as any less creepy to the average user: "They stole my friend's likeness to sell me a lawn chair" still feels slimy.
I'm sure the real reason is that Facebook added a poorly thought out feature to their marketing tools around that time, and someone just decided to try it out.