Speed limits can vary wildly depending on where you are and what the roads are like. Sometimes, it can be as low as 30 mph, 50 is common, 70 typically mostly on highways. I've been through some areas where the limits feel weirdly low. In some cases, I suspect it's deliberate to set speed traps for people passing through who don't know better.
Now obviously, nobody should be pulling 80 in a 30 zone, but in light of some of the speed limits I've personally seen, I absolutely think a hard restriction to the speed limit will cost lives. Maybe it will save others. Maybe even more than it costs. But some will die. Maybe an emergency override would be possible, but of course people will abuse it. I dunno, I'm not sure what the right call is, honestly.