The harsh reality is that the smart shares the roads with SUV's and big rigs so the comparison is fair. If you watch the MB video of the smart and MS sedan hitting head on, you can see the smart holds up remarkably well structurally, but the laws of physics still apply. The smart completely stops and then starts moving backwards, while the larger sedan is till moving forward, so while the stucture is fine the decelleration loads on the occupants in the smart will be much larger.