Racers and hammer rides get the bad rap for crashes, usually due to the speeds and situations they occur in.
However, there's a local pub no-drop ride that about the same time I "graduated up" from that to a new group.........they had a crash 3 weeks in a row. Two crashes within just one of those weeks. Girl broke a collar bone. On a no-drop 15mph pub ride.
People who aren't used to being in tight quarters on bikes, at speed, and don't know the rules/protocols and have no instincts are the problem.
Before I went from "pub group ride" to faster groups, I went to the local slow paceline group knowing the leader was very protective over new riders and great at spending time with them the first time out and teaching them the "norms".
Back to the racers thing. Thing is, you either have "racer instincts" or you don't. You don't have to race to have them. You could be the person in the local slow 50-person deep paceline and have great instincts.
Being exposed to racing and hammer rides though, if you don't have that instinct you WILL be yelled at, made to feel like human filth, and probably not return if you don't get some instincts. People without them either get them or they don't come back. Simple as that.
I think the most dangerous scenario is getting the people without instincts mixed into a large fondo.
A lot of crashes you see in races are caused by outside agitations: dogs, poor course design or signage, person or car onto course, hazard in a corner (sand, debris, etc...).