It's absolutely true that human error can occur, and it does happen sometimes. Of course, nobody is doing big-wall climbing with a grigri (although in Sara Al Qunaibets case there was even a grigri that the coach was able to misuse...). I still feel safer taking a fall with a belayer I trust than I do driving behind some stranger that's driving erratically. The most dangerous part of any climb on pre-bolted route is likely the drive to the crag.