How is that going to happen? We're assuming the AI posts exactly like a human until the comment about Pepsi comes out. It'll be impossible to distinguish from a human, by assumption. Or are you going to just have the site reject everything which mentions Pepsi negatively?

>How is this different from Coca-Cola paying influencers to post negative stuff about Pepsi?

AIs don't need to be paid.

Coca cola can't have millions of influencers on their payroll (or at least, it wouldn't be economically profitable for them to do that). An AI could easily create and post on accounts on a scale that dwarfs real human-generated content.