It doesn't even have to be a human error. Birds in/near cities are happy to attack R/C models. If you see your model you can run away from them, but if you only have the camera view, you won't see what's happening.

Now think that even slightly cracked propeller will easily break off at 10k+ rpm. When this happened for me, piece of the propeller ended up ~10cm under the surface of slightly frozen ground. Fortunately it flew straight down after it broke - I believe it could be lethal if it hit some person instead.

TL;DR, even if you don't make a mistake and can't see a mechanical fault, flying R/C models can be very dangerous. Flying close to people is irresponsible even if you're experienced with controlling them.