It's possible to target ads to a specific audience by exploiting the selection effect that led to your audience existing. This doesn't favour general-audience communities, sure, but I'd honestly be happy with the answer "general-audience things just aren't how the future looks".
But I have no clue what would distinguish (to me) a non-shit ad? Is it saving me money on something I was already going to buy?
Yes. I've been looking for weight equipment over the past year because of the pandemic and gyms being closed and the majority of ads on Instagram are now exercise equipment. I ended up seeing an ad for a company in my country with fairly decent prices and bought a new squat stand. The price difference between the one I bought and the ones I was looking at from companies in the area was around $200. I give up some privacy, they give me targeted ads. Please give me more.
The usual answer to this is to use the context rather than personal information and browsing history. You bring less value to the company advertising their product, but I'd argue that most people are fine with this approach.
The problem is that current incentives lead to a race to the bottom: if some advertisers are less ethical, they can arguably bring more value to their clients, and the ethical advertiser cannot compete anymore.
Contextual advertising, on the other hand, is simple. It shifts the focus away from technology and toward people: recognizing your audience and crafting a message to them, instead of trying to have a computer do it for you. It's old-fashioned marketing.
Perhaps today, but not if we design browser APIs that allow targeting without cross-site tracking: https://github.com/WICG/turtledove https://github.com/WICG/privacy-preserving-ads/blob/main/Par...