I'm in favor of walking.
Personally, I don't think our bodies are meant to run long distances. To me it seems more like we are designed to walk long distances and run/sprint for short distances to avoid danger.
Running is hard on the body, it puts a lot of stress on the joints. As we get older that starts to take a greater toll. I may be a bit biased having already had some joint problems, but I feel that running isn't an ideal exercise. Although, it is possible that with future advances in regenerate medicine, we will be able to regrow cartilage and that will become a non-issue.
"Of all tyrannies, a tyranny exercised for the good of its victims may be the most oppressive. It may be better to live under robber barons than under omnipotent moral busybodies. The robber baron's cruelty may sometimes sleep, his cupidity may at some point be satiated; but those who torment us for our own good will torment us without end, for they do so with the approval of their own conscience." -- C. S. Lewis