SOE is correct, other than the security aspect in some countries, it's a SAFETY issue. Mind you, in my opinion, if the impact is severe enough for a small camera to decapitate someone then it will be severe enough for the heavy overhead bins and their contents (including duty free glass bottles) to come down and maim you too. The problem with some so-called safety issues on aircraft is that they are too selective. CC may rightly ask pax to secure their cameras yet they will ignore overloaded overhead bin issues.
By the way, I have seen a commercial pilot (Captain of a major airline - in uniform) using his camera on landing. Nothing said by CC.