Admitedly, your average american car is not buit for high speed travel. But most cars can handle moving along at a decent rate of 80-90mph. Those cars that cannot, should not be allowed too.
Simply sticking a sign on the side of the road with a number on it is not how speed limits should be set, but thats how they are. Every vehical has different abilities and all roads are not equall, but this is not taken into account.
The other problem is that you can swerve, cut people off, tailgate, never use a turn signal all you want, aslong as it is within the speed limit. Thats just retared. Drivers testing is a joke, if you can handle a parking lot and an empty side street for 5 mins, you can get a license.
Speed itself is not a cause for an accident, it is a modifier. The cause of an accident is someone with a cell phone in one hand and a cheese burger in the other. How many accients are caused because someone simply didn't see the other guy? Basicly all of them, since no one would intentionally hit another car 99% of the time.