Brain surgery is invasive, but the power that the surgeon exercises over the patient is bound to the context of the surgery. Side effects may linger, but the surgeon cannot increase or alter the side effects after the surgery. With Neuralink installed, the owner of the proprietary software that runs on it (because let's be real, there's no way they'd let you control your own brain) has indefinite read and write access to your mind. No thought is private; no action is your own. Everything that happens in your brain happens either because the owners let it, or made it happen.