How LinkedIn does it
LinkedIn explicitly sells visibility. From their own Marketing Solutions help docs: with a "Boost" button click, a Page admin can "instantly turn an organic post into a piece of paid media, amplifying the reach of that message to others outside your immediate network." The recommended minimum spend is $25/day with a 2-day minimum run. According to third-party LinkedIn ad-research, "Promoted Content" (boosted posts) now make up roughly 22% of the LinkedIn feed; LinkedIn Ads make up another 7%. Nearly one in three posts a user sees on LinkedIn is paid-for placement.
The architecture is industry-wide. Twitter/X Premium subscribers get algorithmically boosted reach as part of the subscription. Instagram has Sponsored placements. Facebook has the "Boost Post" button on every page admin's screen. YouTube has Promoted Videos. Substack has paid recommendations. The mechanism is identical across platforms: pay money, your content reaches more people than its organic merit would have earned.
The harm is the legitimacy gradient. A two-tier feed creates a structural disadvantage for creators who refuse to pay (or cannot pay): their organic posts compete against advertisers' boosted content for the same reader's attention, and the platform's ranking weights the paid one heavier. Over time, the feed becomes dominated by content that out-spends, not content that out-earns. The merit gate has been replaced by a payment gate. Visitors looking for the most useful content are served the most-paid-for content instead.