This is why online consumer platforms should be treated as public utilities once they reach a certain size. Amazon’s online shopping arm, youtube, facebook, and gmail are products that clearly meet the bar. Search engines probably do too, at least with respect to web site owners.
Do you intend to ban ranking algorithms?
I think making them optional or auditable would be a start.
I've seen some plausible proposals along those lines. I don't actually think there's sufficient demand for that. The vast majority of people wouldn't want to roll their own spam detection algorithms. And there's only so much an outside source can do to filter spam without giving the enough info that spammers can reverse engineer.