That was his point, or if it wasn't it's my point. It's a physical activity, one that from my POV improves health much more than reduces it. Take the hypothetical where he doesn't ever find a replacement activity, and instead of being fit becomes obese and depressed. that would be worse for society than mountain biking wouldn't it?

For society only; what's the TCO of a mountain biking injury times the rate of injuries, over the TCO of obesity and depression times the likelihood a sedentary lifestyle results?

without access to that data, his anecdote does appear to be a stronger argument than literally no data, no?