Are Porsche 911 cars accident prone?

If you drive them responsibly, no. Actually, the 911 has a much better road holding than most other cars (unless you are comparing it to top Ferrari or Lamborghini models) and great brakes, so I would consider it safer than 'normal' cars. I did not have any problems going ~ 120 mph on a German motorway with slight snow cover with a 996 model Porsche 911 equipped with PSM (Porsche Stability management) - and about 175 mph under good road conditions.