The purpose of trolling and fake comments is not always to directly shift anyone's opinion. It can also be about spreading doubt and confusion by constant repetition of falsehoods, until certain topics and positions that previously were completely unacceptable become an ordinary part of discourse and a viable "view". It's about manipulating and eroding social control mechanisms.

For example, that's how it can become possible for a politician to get elected who openly advocates torture or extrajudicial killings.