A few persons control a large amount of bots. They can manipulate upvotes, downvotes. Silence opinions they don't like, boost the ones they support. They can flood everyone's feed with whatever topic they like. They get to choose what is important, what people get to think about. They can harass any single user, by downvoting posts or being generally unpleasant all the time, and giving the impression that the community agrees. They can create a fake impression of consensus on any given topic.

Now that bots basically pass the Turing test, they can get you to almost never interact with a real person, but instead with machines who never actual learn, listen or change their mind. That sort of thing could erode anyone's opinion of their fellow humans. That could make one think that there's no possibility of common grounds with their adversaries.

Don't underestimate the bots, they're responsible for most of the political turmoil of the last decade.

Owners can use those bots to boost choosen posts/comments with a lot of upvotes or downvote something into oblivion if they don't like something. Bots can be also used for spam and advertising stuff. Overall, if the bots become active the platform will be fucked as the quality of everything will go down. One problem that affects us now is that we lost a reliable way of telling how much factual users are on the platform.

Generally speaking I think people want to interact with other human beings, not bots.

Then there's the questionable morality of it. Companies can profit off bots scraping our info.