There's plenty of reasons to be fearful or suspicious: corporations who develop all the new tech we use today have shown already they don't respect our privacy. Our smartphones, computers, and other Internet connected devices are always harvesting data to advertise to us, so it follows that any brain-implanted device could be used to harvest data for similar purposes. Not everyone gives a shit about this one, but there are plenty who would at least like to be paid for the data that is collected from them and used for profit; barring that we should have the right to forbid data collection without consent.
There are, of course, more sinister applications for brain-implanted devices that can interface with the Internet (and if they don't now, they surely will in the future). I think a lot of us immediately think of the science fiction book and movie, "Minority Report" wherein law enforcement has access to the private thoughts of citizens and arrests and convicts those who have contemplated crime but have not yet perpetrated the crime. Any sane person would never allow the police access to one's private thoughts, let alone a corporation.
Elon Musk has said his ultimate goal with Neuralink goes beyond merely restoring function to injured parts of the body; he wants to make it possible to save and load memories and with those two functions we may also be able to delete memories too. Imagine someone hacking your memories, it could fundamentally alter your perception of yourself and your reality. You could become a prisoner in your own brain, subjected to the censorship of a corporation or government.
These are worst case scenarios and I'm not saying we are there yet, maybe not even close to that level of technology, but we should be aware of what kind of control we may be giving away to a company or authority by allowing such implants to be installed. I hope that we will use it as a means of improving people's lives, but I'm very cautiously optimistic as well.
