TL:DR: Half a million cardiac pacemakers (devices implanted under the skin of your chest to control irregular heartbeats) had a security flaw that would have allowed hackers to alter the patient's heartrate and kill them.
Sure, a chip in the finger might be relatively harmless in comparison, but it could easily be used to track your every movement, even your sleeping patterns. Or maybe they could deliberately overheat it?
If you were a terrorist why would you bother recruiting idiots to blow themselves up when you could finish off a million people at the press of an enter button?
I can foresee a one off 9/11 spectacular before billions of people rip the shit they've had implanted in their bodies out for good. It's going to take something of that magnitude before enough people wake up to what they're exposing themselves to.