418 U.S. military drones have crashed so far. http://www.washingtonpost.com/sf/investigative/2014/06/22/cr... Do you think commercial drones will be better-maintained or have more experienced pilots? I don't.
[0] http://www.theguardian.com/world/2012/jun/12/us-military-min...
I find many of the other comments nearby are carping about details but not really addressing the point, which is that these things can and will crash, which is why they will be regulated somehow.
Also, it's fair to say that the AF doesn't really care about the potential for ground casualties in the event of a mechanical failure.
Let's look at it this way; how many US drones have been captured by enemy forces? Crashing is one thing; falling into the hands of an opponent who can study the device is a mission aspect that the AF and other agencies do care about. More than a handful?