I've pretty much gotten over most of my fear of heights - which is really a fear of being pushed because I have no problem with heights when I'm by myself - but I think standing 4,000 feet above a river on a man-made ledge protected only by a layer of glass would probably send me over the deep end. I don't care if the ledge can withstand the weight of 71 fully loaded Boeing 747 airplanes, 100 mile an hour winds coming from eight directions, and an 8.0 magnitude earthquake from within 50 miles. It's still a man-made ledge covered in glass 4,000 feet up in the air. With lots of people gawping at the view.
I could probably manage it if there were no one else on the platform with me. But what's the likelihood of that happening, eh?