Interesting. Why is it so bad for our joints when it's what we're biomechanically designed for? I started really late - only two years ago at 44 but I thoroughly love it. I don't go far, 5km each morning is enough for me but if I don't go, I really wouldn't be active at all.
It is not bad for your joints. This is mostly a myth. As you said, we are biomechnically designed to run, are extremely good at it. Running is humans super power. When you watch a nature documentary and hear about a spider that can lift 100x its body weight, or a whale that can hold its breath for 3 hours, or a bird that can nose dive at 200 MPH... - well humans ability to run is almost unmatched in the entire animal kingdom.
As has been mentioned several times in this thread, you gain run fitness quickly but it takes longer for your bones and muscles to adapt. Most beginners run far to fast and ramp up volumes and paces way to quickly. Injury is inevitable and then these people go on to complain that running ruins their knees/is bad for you, spreading myths