Part of the reason a bot will be used by a broker is where a stock is illiquid. Whether to accumulate or distribute the use of a Bot will ensure the price of the stock is not unduly affected by the seller/buyers actions.
On a more general note, walking the price has happened since exchanges began, its just now been automated instead of dealer teams. I have no issues with bots, they do a job, if they turn them off it'll be humans doing it again.
