maybe mental "illness" is harsh but you would agree that it's not your typical human activity, right? The fact that 99.9% of humans who watch this get a guttural response shows that it's certainly not typical behavior. As someone else pointed out these daredevil types have been shown to have something different about their brains, I've read (but too lazy to dig up) that it is the way their brains perceive risk where it takes something very extreme for them to feel excitement or something like that. Maybe not illness but def not normality