Yeah I have to agree with Max on that one. There are some wide skis that are made like GS skis (Stockli used to make several) that rail on hard snow and are incredibly stable. But most wide skis today have some amount of rocker, a lot less metal and they are by no means more stable than a thin GS ski with huge amounts of metal. There really isn't an argument here, it's just simple physics. The more metal the more stable and while there may be some wide skis with as much metal as a GS ski today they are few and far between, and most people can't ski on them anyway.
I agree with this and Max I am sorry about your friend, that just should not happen as much as it does.
But I really don't think it has to do with fat skis. Most people thankfully never go fast enough to test the limits of their ski design. I think much of the problem is an unwillingness of ski slopes to use their ski patrols to enforce a skiers responsibility code. They are doing a better job of writing it up and putting it on their ski maps etc. I just rarely see it being enforced on the hill.
What is everyone else seeing out there?