The dangers of being hit by another car are far in excess of the dangers of hitting a wall by yourself. You don’t know exactly where the other car is going to hit you, for example – I wouldn’t want an F1 car travelling at 150mph into the side of my monocoque regardless of how stringent the crash tests are. Remember how Alessandro Zanardi lost his legs or Paul Dana was killed (not F1 but they illustrate the point).
Plus Piquet’s crash was premeditated – he knew what he was doing, whereas Webber presumably didn’t plan to crash. A better comparison would be with Schumacher’s Monaco parking incident, where he made a mess of the last corner and exploited it to disadvantage everyone else as well. And as we know, Schumacher actually avoided doing any damage to his car at all – in those situations self-preservation has to take a high priority. Regardless of the heat of the moment or whatever, Webber would not have risked his life attempting to collect a championship rival.
In short, it’s a very stupid theory.