There have been many incidents over the years where cars ended up in the crowds but look at the way things were and its easy to see why it used to happen. Motorsport is very very safe in comparison today so we can't image what the conditions were like back then.
I am sure it was this accident that lead to the motorsport ban in Austria.
I remember the terrible accident in Portugal when one of the Ford RS200's ploughed into the crowds, 14 were killed. Years later driving for FIAT in Argentina I saw first hand just how mad some of the spectators can be filling the road in front of you, only moving at the last moment and trying to touch car as you pass! By then in Europe things had got a lot better with spectator control although it can still be a bit hairy.
Back to the Le mans incident, its hard to blame Mike Hawthorne, the guy in the Healey should have backed off and not turned infront of the Merc. Sadly today, if it were to happen, 2 cars would be out of a race and some cross words said and put down to "a racing incident"