I have no idea what the number would be, and probably no one else does either. I don't think the real issue is the total numbers though, it's always the outliers that are the problem -- as someone below stated: "jerks ruin everything".

The vast majority of hobbyists are thoughtful and considerate. RC aircraft have existed for a long time with few problems, with many of those aircraft being considerably larger, faster and higher flying.

It's the few users that don't consider the ramifications of their actions, like in the video I posted, which can ruin it for everyone.