That's the point, spectators rarely cause crashes and in my 40 years of watching the tour have never caused anything like this that I remember.
Tour crowds are, like crowds at the Ryder Cup, Wimbledon on the outer courts, or most high profile sporting occasions now I think about it, highly knowledgable.
One of the cardinal sins is to turn your back on the riders, especially the peloton. And why would you when you are there to see them!!!
When the crowds close in on the riders, usually near the tops of climbs, there's usually less danger than it seems.
One rider (maybe 2 now, not sure) had to retire because of injuries, a couple of favourites lost significant time and reigning champ, Pogabar's right-hand man, Marc Hirschi, separated his shoulder and will probably have a lot less value.
And it could have been so much worse.
As for policing a course that's over 2,000 miles long, well, that's literally impossible and it's the insane crowds that make the Tour what it is,
There are no charges being filed against the woman and the Tour have dropped an attempt to sue her, but she really needs to keep away from organized sport.
There is nothing either good or bad, but thinking makes it so.