Those sponsored posts appear next to whatever appears in the user's feed. If a user follows a bunch of cat photos, then the sponsored post appears next to cat photos. If the user follows a bunch of NASCAR related accounts it appears next to NASCAR. The ad company has little agency over this.

I don't think advertising companies would really see this as an issue. It's not like an ad playing before a video where sponsorship can be directly tied to a piece of content. The content adjacent to ads is determined by users' viewing habits and follows.

Or - a user follows a public figure out of good-faith interest, one of their tweets sparks controversy, and the replies get bad-faith violent (happens all the time). Then the next post is an ad for toothpaste. Colgate's not going to be happy to associate their product with vitriol.

Ultimately, YouTube users have a higher degree of control over what they consume, because they self select each video on a drop-by-drop level; on Twitter the user only curates which hoses they get blasted by. And we know that YouTube still struggles with ad suitability.

I think you're still not getting it. Sponsored posts aren't part of a chronological feed. They're not associated with any specific content. It's probably not this simple, but it's essentially that every 20 posts a user sees a sponsored post. The posts adjacent to the sponsored post are determined entirely by who the user follows.

For users that don't follow this public figure, the Colgate ads are going to appear somewhere else. If someone takes a screenshot and sends it to Colgate, Twitter will say "hey, it was that user's decision to follow these toxic people."