Another point...most of the crew are really, really overworked! They don't have time to do anything. As has been mentioned before...there are cameras everywhere...the crew and staff are watched closely...and ANY complaint is taken very very seriously!! At least on any of the major cruise lines.
On the cruise ships we've been on....HAL, RCCI and Celebrity...the crew and staff were always professional...and we could tell, they were very aware that their conduct was always being observed by other staff and crew.
I'm not saying that it couldn't happen...didn't happen, or hasn't happen...but I think that over all...the incidents of accidental falling overboard are because of a passenger being drunk...rather than a crew member tossing a passenger over the rail.