I was in an accident two weeks ago due to a SS like this. SS stops abruptly and for no apparent reason on an exit ramp. I slam on my brakes, move my car to the side as much as possible and guy behind me, hits me and pushes me into car in front of me. Which then, sped up and off and away, nowhere to be found. What was especially infuriating was that the cops told me that they weren't going to look too hard for him as I and the driver behind me were 100% at fault, automatically, according to the laws of the state. Yes, the person in front of you can stop for no reason and if you hit them, it's always your fault.
This is the case in a lot of places, and it's a monumentally stupid idea. It's right up there with the various "pedestrian is never at fault" rules you get various places.
I got a lovely little lecture about MY responsibility to always leave enough room to compensate for someone stopping dead in front of me and someone hitting me in the rear so as to "save" the idiot in front of me.
I will bet serious cash money that the cop who lectured you regularly does not practice what he preaches. No one leaves that much space between them and the car in front of them under all conditions. Our society literally would not function if everyone did. You just use your best judgment and assume the person in front of you isn't a suicidal moron. Sadly, that's not always a safe assumption.
I'm reminded of a time I had a cop tailgating me late at night. Really, seriously tailgating me in a way that was incredibly intimidating and unsafe. I wanted very badly to slam on my brakes and see just how far that "car in the rear is always to blame" thing would take me. My car was an absolute beast, it would've been fine, and we weren't going fast enough to cause major injury to anything but the cop's front end. Luckily I was smart enough to decide to turn off into a handy housing development and let the cop get ahead of me.
I gave myself a few minutes to calm down and the cop time to get far ahead of me and then went back to driving home. I came around a corner to a stop sign and there was the cop, stopped at the sign to my left, pointing the way I was headed. I waited, since he had the right of way, and he just sat there for several seconds revving his engine. I finally made my turn and he started following me again, still too close but not dangerously so. He finally let me go when we got to a major road. I really should've reported that idiot, but it wouldn't have done any good.